Improve docs on how to hack using linux distros

Author: berinhard

.gitignore

@@ -30,4 +30,5 @@ zamples
 misc/windowsexecutablestub/Debug
 misc/windowsexecutablestub/Release
 *.sdf
-*.suo
+*.suo
+linux/

HOWTO-HACK.txt

@@ -41,12 +41,15 @@ the original repo:
 
     $ git clone https://github.com/jdf/processing.py.git
 
-  
+
 You'll need source for processing and processing-video.
 
     $ git clone --depth=1 https://github.com/processing/processing.git
     $ git clone --depth=1 https://github.com/processing/processing-video.git
 
+If you are a Linux user, you'll also have to create a directory named `linux`
+inside your `processing.py` directory.
+
 Then, to sanity-check your environment and run all of Python Mode's
 integration tests, do the following: