Add docs

keyboard/planck/keymaps/cbbrowne/readme.md

@@ -29,6 +29,7 @@ doing sundry experimentation:
      in a more useful context.
    - Key [2][2] aka "a" uses a random number generator to select a digit 0-9 at random
    - Key [3][2] aka "z" uses a random number generator to select a letter a-z at random
+   - Key [1][3] aka "e" spits out the keymap version number
 
 2. Some code structure ideas
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