Update README.md

How to compile.

README.md

@@ -2,10 +2,18 @@
 A python version of Space Invaders
 
 ### How to run
-* Python 2.7 and latest PyGame are required
-* Clone the repo or download it
-* Run PythonInvaders with `python PythonInvaders.py` in a terminal/command prompt
-* The application is graphical, so it probably won't work in a CLI environment
+1. Python 2.7 and latest PyGame are required
+2. Clone the repo or download it
+3. Run PythonInvaders with `python PythonInvaders.py` in a terminal/command prompt
+4. The application is graphical, so it probably won't work in a CLI environment
 
 ### How to compile
-* I will publish a script for building into .exe using py2exe soon
+To compile PythonInvaders into a self-contained .exe file, perform the following steps:
+1. Make sure you have the following installed on you computer:
+  * Python 2.7
+  * PyGame
+  * Py2exe
+2. Edit compile.py to match your own information, don't use my name/email please
+3. Backup any local changes, as the script may ruin your stuff
+4. Run the script with `python compile.py`
+5. The .exe should be created.