Disable parallel make

A problem that I observed (ages ago but only recently noted) in the
mkiocccentry repo is that make -j does not work right. It is highly
likely that this will be a problem here too so I have set this up now
for later on.

Makefile

@@ -1,3 +1,12 @@
+# Disable parallel Makefile execution
+#
+# We do not support parallel make.  We have found most
+# parallel make systems do not get the rule dependency order
+# correct, resulting in a failed attempt to compile.
+#
+.NOTPARALLEL:
+
+
 # compile do-nothing jparse.c - hopefully placate the GitHub workflow for now
 all: jparse.c
 	${CC} jparse.c -o jparse