Added information on add-ons.

git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@1201 8092fc87-c524-0410-9efc-e669fe64eaf9

sc2/doc/users/manual.txt

@@ -96,6 +96,11 @@ Use the .MOD based PC soundtrack everywhere.
 Can be "high", "medium", or "low".  Specifies how nice the audio
 sounds.  Slower machines should lower the audio quality.
 
+	--addon <addon>  (no short version)
+
+Replace <addon> by the name of an add-on to enable in the game. See
+the section 'ADD-ONS' below for details.
+
 	--sound          (no short version)
 
 Can be "openal", "mixsdl" or "none". Specifies which driver/mixer
@@ -543,3 +548,25 @@ Later versions of The Ur-Quan Masters will include a key configuration
 tool.  In the meantime, the keys.cfg has a bunch of comments in it
 that should help you set up your joystick and remap key controls to
 your satisfaction.
+
+
+			   ADD-ONS
+
+Version 0.3 of The Ur-Quan Masters has basic support for add-on packages.
+Though it is not very elaborate yet, you can install some content add-ons.
+
+Inside the directory where the content is installed, in the content/packages/
+directory, there is a directory 'addons/'. In this directory, you can
+create new directories with .zip files to be used in addition to the
+standard content .zip files.
+When you specify the command-line option '--addon <addon>', the .zip files
+inside the directory content/packages/addons/<addon> will be included
+in the game. '--addon' may be specified more than once to enable multiple
+add-ons.
+
+At the time this version of The Ur-Quan masters is released, there aren't
+any official add-ons yet. Keep an eye on http://uqm.sf.net/ for those.
+Our boards, which can be found on this site too, are a good place
+to start looking for unofficial ones.
+
+