A little documentation.

rakefile

@@ -174,6 +174,8 @@ end
 desc "Install all python prerequisites for the lms and cms"
 task :install_python_prereqs do
     sh('pip install -r requirements.txt')
+    # Check for private-requirements.txt: used to install our libs as working dirs,
+    # or personal-use tools.
     if File.file?("private-requirements.txt")
         sh('pip install -r private-requirements.txt')
     end