Update readme to suggest ./configure instead of printf

This also makes some other minor cleanups:
- Suggest `python x.py` on windows instead of `./x.py`, which usually
  doesn't work
- Move the "Configure and Make" section to a subsection of "Building on
  Unix"
- Mention `config.toml` earlier
- Suggest `x.py setup user` on Windows, since `configure` won't work

Author: jyn514

Diff for: README.md

@@ -22,6 +22,8 @@ Read ["Installation"] from [The Book].
 
 The Rust build system uses a Python script called `x.py` to build the compiler,
 which manages the bootstrapping process. It lives at the root of the project.
+It also uses a file named `config.toml` to determine various configuration settings for the build.
+You can see a full list of options in `config.example.toml`.
 
 The `x.py` command can be run directly on most Unix systems in the following
 format:
@@ -85,6 +87,8 @@ See [the rustc-dev-guide for more info][sysllvm].
 
 ### Building on a Unix-like system
 
+#### Build steps
+
 1. Clone the [source] with `git`:
 
    ```sh
@@ -96,18 +100,13 @@ See [the rustc-dev-guide for more info][sysllvm].
 
 2. Configure the build settings:
 
-   The Rust build system uses a file named `config.toml` in the root of the
-   source tree to determine various configuration settings for the build.
-   Set up the defaults intended for distros to get started. You can see a full
-   list of options in `config.example.toml`.
-
    ```sh
-   printf 'profile = "user" \nchangelog-seen = 2 \n' > config.toml
+   ./configure
    ```
 
    If you plan to use `x.py install` to create an installation, it is
    recommended that you set the `prefix` value in the `[install]` section to a
-   directory.
+   directory: `./configure --set install.prefix=<path>`
 
 3. Build and install:
 
@@ -117,12 +116,25 @@ See [the rustc-dev-guide for more info][sysllvm].
 
    When complete, `./x.py install` will place several programs into
    `$PREFIX/bin`: `rustc`, the Rust compiler, and `rustdoc`, the
-   API-documentation tool. If you've set `profile = "user"` or
-   `build.extended = true`, it will also include [Cargo], Rust's package
-   manager.
+   API-documentation tool. By default, it will also include [Cargo], Rust's package manager.
+   You can disable this behavior by passing `--set build.extended=false` to `./configure`.
 
 [Cargo]: https://github.com/rust-lang/cargo
 
+#### Configure and Make
+
+This project provides a configure script and makefile (the latter of which just invokes `x.py`).
+`./configure` is the recommended way to programatically generate a `config.toml`. `make` is not
+recommended (we suggest using `x.py` directly), but it is supported and we try not to break it
+unnecessarily.
+
+```sh
+./configure
+make && sudo make install
+```
+
+`configure` generates a `config.toml` which can also be used with normal `x.py` invocations.
+
 ### Building on Windows
 
 On Windows, we suggest using [winget] to install dependencies by running the
@@ -186,7 +198,7 @@ toolchain.
 4. Navigate to Rust's source code (or clone it), then build it:
 
    ```sh
-   ./x.py build && ./x.py install
+   python x.py setup user && python x.py build && python x.py install
    ```
 
 #### MSVC
@@ -204,6 +216,7 @@ With these dependencies installed, you can build the compiler in a `cmd.exe`
 shell with:
 
 ```sh
+python x.py setup user
 python x.py build
 ```
 
@@ -232,21 +245,7 @@ Windows build triples are:
 
 The build triple can be specified by either specifying `--build=<triple>` when
 invoking `x.py` commands, or by creating a `config.toml` file (as described in
-[Installing from Source](#installing-from-source)), and modifying the `build`
-option under the `[build]` section.
-
-### Configure and Make
-
-While it's not the recommended build system, this project also provides a
-configure script and makefile (the latter of which just invokes `x.py`).
-
-```sh
-./configure
-make && sudo make install
-```
-
-`configure` generates a `config.toml` which can also be used with normal `x.py`
-invocations.
+[Building on a Unix-like system](#building-on-a-unix-like-system)), and passing `--set build.build=<triple>` to `./configure`.
 
 ## Building Documentation