rollup merge of #22395: brson/readme-cleanup

Just a few things to make the README ever more perfect.

r? @steveklabnik

Author: alexcrichton

README.md

@@ -1,14 +1,16 @@
 # The Rust Programming Language
 
 This is a compiler for Rust, including standard libraries, tools and
-documentation.
+documentation. Rust is a systems programming language that is fast,
+memory safe and multithreaded, but does not employ a garbage collector
+or otherwise impose significant runtime overhead.
 
 ## Quick Start
 
-Read ["Installing Rust"][install] from [The Book][trpl].
+Read ["Installing Rust"] from [The Book].
 
-[install]: http://doc.rust-lang.org/book/installing-rust.html
-[trpl]: http://doc.rust-lang.org/book/index.html
+["Installing Rust"]: http://doc.rust-lang.org/book/installing-rust.html
+[The Book]: http://doc.rust-lang.org/book/index.html
 
 ## Building from Source
 
@@ -19,22 +21,14 @@ Read ["Installing Rust"][install] from [The Book][trpl].
     * `curl`
     * `git`
 
-2. Download and build Rust:
-
-    You can either download a [tarball] or build directly from the [repo].
-
-    To build from the [tarball] do:
-
-        $ curl -O https://static.rust-lang.org/dist/rustc-nightly-src.tar.gz
-        $ tar -xzf rustc-nightly-src.tar.gz
-        $ cd rustc-nightly
-
-    Or to build from the [repo] do:
+2. Clone the [source] with `git`:
 
         $ git clone https://github.com/rust-lang/rust.git
         $ cd rust
 
-    Now that you have Rust's source code, you can configure and build it:
+[source]: https://github.com/rust-lang/rust
+
+3. Build and install:
 
         $ ./configure
         $ make && make install
@@ -46,7 +40,10 @@ Read ["Installing Rust"][install] from [The Book][trpl].
 
     When complete, `make install` will place several programs into
     `/usr/local/bin`: `rustc`, the Rust compiler, and `rustdoc`, the
-    API-documentation tool.
+    API-documentation tool. This install does not include [Cargo],
+    Rust's package manager, which you may also want to build.
+
+[Cargo]: https://github.com/rust-lang/cargo
 
 ### Building on Windows
 
@@ -72,9 +69,6 @@ $ pacman -S base-devel
         $ ./configure
         $ make && make install
 
-[repo]: https://github.com/rust-lang/rust
-[tarball]: https://static.rust-lang.org/dist/rustc-nightly-src.tar.gz
-
 ## Notes
 
 Since the Rust compiler is written in Rust, it must be built by a
@@ -94,9 +88,9 @@ supported build environments that are most likely to work.
 Rust currently needs about 1.5 GiB of RAM to build without swapping; if it hits
 swap, it will take a very long time to build.
 
-There is a lot more documentation in the [wiki].
+There is more advice about hacking on Rust in [CONTRIBUTING.md].
 
-[wiki]: https://github.com/rust-lang/rust/wiki
+[CONTRIBUTING.md]: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md
 
 ## Getting help
 
@@ -114,6 +108,14 @@ The Rust community congregates in a few places:
 
 To contribute to Rust, please see [CONTRIBUTING.md](CONTRIBUTING.md).
 
+Rust has an [IRC] culture and most real-time collaboration happens in a
+variety of channels on Mozilla's IRC network, irc.mozilla.org. The
+most popular channel is [#rust], a venue for general discussion about
+Rust, and a good place to ask for help,
+
+[IRC]: https://en.wikipedia.org/wiki/Internet_Relay_Chat
+[#rust]: irc://irc.mozilla.org/rust
+
 ## License
 
 Rust is primarily distributed under the terms of both the MIT license