Update readme for installation instructions from wiki (#21)

* Copy contents of wiki https://github.com/Thinkofname/steven/wiki/Compiling-and-or-running

* Update and cleanup install instructions: now uses MSVC instead of MinGW on Windows, and no longer uses OpenSSL (https://github.com/iceiix/steven/issues/2)

README.md

@@ -17,18 +17,73 @@ In action: http://gfycat.com/NeedyElaborateGypsymoth
 I generally am on the `irc.spi.gt` irc network in the `#think` channel.
 Feel free to pop in to say hi, [Webchat can be found here](https://irc.spi.gt/iris/?channels=think)
 
-## Building
+## Downloads
-For more detailed info and platform specific instructions check the [wiki](https://github.com/Thinkofname/steven-rust/wiki/Compiling-and-or-running).
-
-Currently requires SDL2, and **beta or nightly** Rust to build.
-
-`cargo build --release`
 
 Windows users can download pre-compiled builds from here: https://ci.appveyor.com/project/iceiix/steven
 (Select your platform, Click the artifacts tab and download Steven.zip)
 
 The Visual Studio 2015 Redistributable is required to run these builds.
 
+## Building
+
+Currently requires SDL2, and **beta or nightly** Rust to build.
+
+Compile and run:
+```bash
+cargo run --release
+```
+Just compile:
+```bash
+cargo build --release
+```
+
+If you get an error such as:
+
+```
+  = note: ld: library not found for -lSDL2                                                                                                                                                                                                   
+          clang: error: linker command failed with exit code 1 (use -v to see invocation)     
+```
+
+then you need to install the prerequisites, see below:
+
+### Prerequisites
+
+Compiling `steven` requires Rust beta and SDL2. Instructions for setting up SDL2 is platform-specific and will be covered as such outside of this section. 
+
+An easy way to manage multiple Rust toolchains is [`rustup`](https://github.com/rust-lang-nursery/rustup.rs). Installation instructions for `rustup` can be found on its [website](https://www.rustup.rs/).
+
+Once you've set up `rustup`, grab Rust beta by running
+```sh
+rustup install beta
+```
+
+Now we need to make sure that `steven` is compiled with beta. To do this without making beta the default across the entire system, run the following command in the `steven` directory:
+```sh
+rustup override set beta
+```
+
+### Installing dependencies on Linux
+Install SDL2 (with headers) via your distro's package manager. Packages with headers generally end with `-dev`.
+For example on Debian-based systems such as Ubuntu Linux:
+
+```bash
+apt-get install -y libsdl2-dev libsdl2-mixer-dev gcc libegl1-mesa-dev libgles2-mesa-dev
+```
+
+### Installing dependencies on OS X
+Installing them is easiest with [Homebrew](http://brew.sh/). To install SDL2 issue this command:
+
+```bash
+brew install sdl2
+```
+
+### Installing dependencies on Windows
+Build with Visual Studio 2015. May build with other compilers, but not tested
+(previously was built with MinGW and the GNU toolchain).
+
+Download [SDL2-devel-2.0.4-VC.zip](https://www.libsdl.org/release/SDL2-devel-2.0.4-VC.zip), extract and
+copy SDL2-2.0.4\lib\x64\SDL2.lib to C:\Rust\lib\rustlib\x86_64-pc-windows-msvc\lib\SDL2.lib.
+
 ## Running
 
 ### Standalone