address review comments

Author: mark-i-m

src/building/prerequisites.md

@@ -1,15 +1,42 @@
 # Prerequisites
 
+## Dependencies
+
 Before building the compiler, you need the following things installed:
 
-* Python
-* A C/C++ compiler toolchain
-* cmake
-* rustc
+* `g++` 5.1 or later or `clang++` 3.5 or later
+* `python` 3 or 2.7
+* GNU `make` 3.81 or later
+* `cmake` 3.4.3 or later
+* `curl`
+* `git`
+* `ssl` which comes in `libssl-dev` or `openssl-devel`
+* `pkg-config` if you are compiling on Linux and targeting Linux
+
+Additionally, if you want to build `rustc` with your system's LLVM, you will
+need `llvm-config`. See [this section for more info][sysllvm].
+
+[sysllvm]: ./suggested.md#building-with-system-llvm
+
+## Hardware
+
+These are not so much requirements as _recommendations_:
+
+* ~15GB of free disk space (~25GB or more if doing incremental builds).
+* >= 8GB RAM
+* >= 4 cores
+* Internet access
+
+Beefier machines will lead to much faster builds. If your machine is not very
+powerful, a common strategy is to only use `./x.py check` on your local machine
+and let the CI build test your changes when you push to a PR branch.
 
 ## `rustc` and toolchain installation
 
-Follow the installation given in the [Rust book](https://doc.rust-lang.org/book/ch01-01-installation.html) to install a working `rustc` and the necessary C/++ toolchain on your platform.
+Follow the installation given in the [Rust book][install] to install a working
+`rustc` and the necessary C/++ toolchain on your platform.
+
+[install]: https://doc.rust-lang.org/book/ch01-01-installation.html
 
 ## Platform specific instructions