Add to developer doc page

Author: edwardchalstrey1

doc/developer.catalog.rst

@@ -11,8 +11,8 @@ Currently supported representations are:
 - `.efg` for extensive form games
 - `.nfg` for normal form games
 
-Add new games
--------------
+Add new game files
+------------------
 
 1. **Create the game file:**
 
@@ -43,3 +43,18 @@ Add new games
    .. warning::
 
       Make sure you commit all changed files e.g. run ``git add --all`` before committing and pushing.
+
+Code new games & add game families
+----------------------------------
+
+1. **Add the game code:**
+
+   Open `catalog/families.py` and create a new function, or modify an existing one. Ensure your function returns a ``Game`` object.
+   You may wish to vary the game title and/or description based on the chosen parameters.
+
+2. **Update the catalog:**
+
+   Update the dictionary returned by ``family_games()`` in `catalog/families.py` with all variants of your game(s) you want in the catalog.
+   Ensure each entry has unique game slug as key (this will be used by ``pygambit.catalog.load('slug')``), and returns a call of the function with specific parameters.
+
+3. **Submit a pull request to GitHub with all changes.**