Create README.md and fix various spelling errors

Signed-off-by: Jeffrey H. Johnson <trnsz@pobox.com>

INFO

@@ -26,7 +26,7 @@ reappears.  They also have a bug that if you type a meta character the
 character that gets sent is shifted and if you type meta shift character
 it sends a lowercase character.  There is nothing I can do about this.
 
-For some reason talk, amoung a few other things, core dumps when
+For some reason talk, among a few other things, core dumps when
 supduping in from a lisp machine (either a 3600 or a cadr).  I've seen
 the same bug a BBN bitgraph.  It seems to be a bug with programs which
 use curses and is evoked by large screen sizes.

README.md

@@ -1 +1,93 @@
-![](https://travis-ci.org/larsbrinkhoff/lbForth.svg?branch=master)
+# `supdup`
+
+## Overview
+
+* `supdup` is a client (and `supdupd` is a server) implementing the SUPDUP (*Sup*er *Dup*er TELNET) protocol, a highly efficient [TELNET](https://www.rfc-editor.org/rfc/rfc854.txt)-style remote display protocol, on UNIX-like systems.
+
+* It originated as a private protocol between the [Chaosnet](https://chaosnet.net/)-connected ITS systems at MIT to allow a user at any one of these systems to use one of the others as a display; later implementations were developed for [various platforms](https://gunkies.org/wiki/Chaosnet#Protocol_implementations).
+
+* The software supports connections over TCP/IP and Chaosnet (optionally using the [cbridge](https://github.com/bictorv/chaosnet-bridge) software).
+
+## Supported platforms
+
+* Tested operating systems: Oracle Solaris, OpenIndiana illumos, Linux/musl, Linux/glibc, IBM AIX, IBM OS/400 (PASE), Haiku, FreeBSD, OpenBSD, NetBSD, and Apple macOS.
+
+## Supported compilers
+
+* Tested compilers: PCC, GCC, Clang, Xcode, IBM XL C, IBM Open XL C, Oracle Studio C, NVIDIA HPC SDK C, Portland Group C, and DMD ImportC.
+
+## Building the `supdup` client
+
+### Generic UNIX
+
+* Building on generic UNIX-like systems (**Linux**, **\*BSD**, **macOS**, **Haiku**, etc.):
+  * Install prerequisite packages:
+    * Required: `make` (GNU), `ncurses` (libraries and headers),
+    * Recommended: `pkg-config`
+  * Build: `gmake` (or sometimes just `make`)
+[]()
+
+[]()
+* The usual environment variables (*e.g.* `CC`, `CFLAGS`, `LDFLAGS`, etc.) are respected, for example:
+  * `env CC="gcc" CFLAGS="-Wall" LDFLAGS="-L/usr/local" gmake`
+
+### IBM AIX
+
+* Building on IBM AIX 7:
+  * Install prerequisite packages:
+    * `dnf install make ncurses-devel pkg-config`
+  * Build with GNU GCC:
+    * `env CC="gcc" CFLAGS="-maix64" LDFLAGS="-maix64 -Wl,-b64" gmake`
+  * Build with IBM XL C V16:
+    * `env CC="xlc" CFLAGS="-q64" LDFLAGS="-q64" gmake`
+  * Build with IBM Open XL C V17:
+    * `env CC="ibm-clang" CFLAGS="-m64" LDFLAGS="-m64" gmake`
+
+### IBM i (OS/400)
+
+* Building on PASE for IBM i (OS/400):
+  * Install prerequisite packages:
+    * `yum install gcc10 make-gnu ncurses-devel pkg-config`
+  * Build with GNU GCC:
+    * `env CC="gcc-10" CFLAGS="-maix64" LDFLAGS="-maix64 -Wl,-b64" gmake`
+
+### DMD ImportC
+
+* Building with DMD ImportC:
+  * `dmd -betterC -c -of=supdup.o chaos.c charmap.c supdup.c tcp.c $(pkg-config --cflags-only-I ncurses)`
+  * `cc -o supdup supdup.o $(pkg-config --libs ncurses)`
+
+## Building the `supdup` server
+
+* An *experimental* server, `supdupd`, is included.
+* The server component is *incomplete* (and *may not* build on all platforms).
+[]()
+
+[]()
+* To build the server on generic UNIX-like systems:
+  * Install prerequisite packages: `make` (GNU)
+  * Build: `gmake` (or sometimes just `make`)
+
+## Bug Reporting
+
+* To report a problem with `supdup`, use GitHub Issues:
+  * https://github.com/PDP-10/supdup/issues/new/choose
+
+## External links
+
+### SUPDUP
+
+* [RFC 734: SUPDUP Protocol](https://www.rfc-editor.org/rfc/rfc734.txt)
+* [RFC 736: TELNET SUPDUP Option](https://www.rfc-editor.org/rfc/rfc736.txt)
+* [RFC 746: The SUPDUP Graphics Extension](https://www.rfc-editor.org/rfc/rfc746.txt)
+* [RFC 747: Recent Extensions to the SUPDUP Protocol](https://www.rfc-editor.org/rfc/rfc747.txt)
+* [RFC 749: TELNET SUPDUP-OUTPUT Option](https://www.rfc-editor.org/rfc/rfc749.txt)
+* [AI Memo 643: A Local Front End for Remote Editing](http://www.bitsavers.org/pdf/mit/ai/aim/AIM-643.pdf)
+* [AI Memo 644: The SUPDUP Protocol](http://www.bitsavers.org/pdf/mit/ai/aim/AIM-644.pdf)
+* [PuTTY: SUPDUP Backend](https://git.tartarus.org/?p=simon/putty.git;a=blob;f=otherbackends/supdup.c;h=6f574c9fb9c34b1307b67326038aa713c2b1d07a;hb=HEAD)
+
+### Chaosnet
+
+* [AI Memo 628: Chaosnet](http://bitsavers.org/pdf/mit/ai/AIM-628_chaosnet.pdf)
+* [Chaosnet Bridge](https://github.com/bictorv/chaosnet-bridge)
+* [Chaosnet Wiki](https://chaosnet.net/)

supdup.c

@@ -1048,7 +1048,7 @@ suspend (void)
   tcsetattr(0, TCSANOW, &otio);
 #endif
   (void) mode (save);
-  *netfrontp++ = ITP_ESCAPE;      /* Tell other end that it sould refresh */
+  *netfrontp++ = ITP_ESCAPE;      /* Tell other end that it should refresh */
   *netfrontp++ = ITP_PIATY;       /* the screen */
   restore ();
 }

supdupd.c

@@ -881,31 +881,30 @@ void do_crlf (void)
 /* base state */
 #define RS_DATA		0
 
-/* recieved ITP_ESCAPE (034) Waiting for `m' */
+/* Received ITP_ESCAPE (034) Waiting for `m' */
 #define RS_ITP_ESCAPE	1
-/* received ITP_ESCAPE, `m'>#o100
+/* Received ITP_ESCAPE, `m'>#o100
    Waiting for `n'.
    Char will be (+ (* (- `m' #o100) #o200) `n') */
 #define RS_BUCKY	2
 
-/* Recived ITP_ESCAPE, ITP_FLOW_CONTROL_INCREASE
+/* Received ITP_ESCAPE, ITP_FLOW_CONTROL_INCREASE
    Ignore next char, since un*x can't hack real, winning, flow control */
 #define RS_FLOW_CONTROL_INCREASE 3
 
-/* Recived ITP_ESCAPE, ITP_CURSORPOS
+/* Received ITP_ESCAPE, ITP_CURSORPOS
    Waiting for `row' */
 #define RS_CURSORPOS_1	4
-/* Recived ITP_ESCAPE, ITP_CURSORPOS, `row'
+/* Received ITP_ESCAPE, ITP_CURSORPOS, `row'
    Waiting for `column' */
 #define RS_CURSORPOS_2	5
 
-/* received SUPDUP_ESCAPE (#o300)
+/* Received SUPDUP_ESCAPE (#o300)
    Waiting for `m' */
 #define RS_SUPDUP_ESCAPE 6
 
-/* received SUPDUP_ESCAPE, SUPDUP_LOCATION.
-   Now receiving 000-terminated
-   location string */
+/* Received SUPDUP_ESCAPE, SUPDUP_LOCATION.
+   Now receiving 000-terminated location string */
 #define RS_LOCATION	7
 
 void suprcv (void)