Expand the README.md a tad.

Signed-off-by: Adrian Conlon <adrian.conlon@gmail.com>

README.md

@@ -4,3 +4,32 @@ Gameboy emulator
 Plays Tetris, lots of bugs!
 
 Uses the Blargg Gb_Snd_Emu library. Sound is now the best part of this emulator!
+
+# Ubuntu Linux
+
+## Prerequisites
+
+### Build prerequisites
+
+`apt-get install build-essential libsdl2-dev libsdl2-mixer-dev libboost-dev`
+
+### ROMs required
+
+1. Original Gameboy boot ROM: "DMG_ROM.bin"
+	1. Place in the "roms" folder
+1. Game ROM (e.g. Tetris): "Tetris (World).gb"
+	1. Place in the "roms/games" folder
+
+## Obtaining source
+
+`git clone /~https://github.com/MoleskiCoder/gb.git`
+`cd gb`
+`git submodule update --init --recursive`
+
+## Building
+
+`make`
+
+## Running
+
+`src/gb`