All the Dash cheat sheets that can be installed from Preferences > Downloads > Cheat Sheets can be found in this repo. You can modify them or add new ones using pull requests.
Cheat sheets are generated using cheatset. Check out cheatset's README for instructions on how to make your own cheat sheet.
To modify an existing cheet sheet, simply fork this repo and look inside the "cheatsheets" folder. The format used to define a cheat sheet is quite simple, so don't be afraid to jump right in.
1. Naming
All the categories, commands and names in your cheat sheet will be inserted in the search index and will be searchable within Dash. Try to keep these entries as concise as possible and complement them with notes if more details are required.
2. Title Case
Try to use Title Case only for categories. Anything else should be Normal/Sentence case. This also applies to menu item names, which should be converted to Normal/Sentence case.
3. Keyboard shortcuts (if any)
Try not to include really common keyboard shortcuts (e.g. Copy, Paste, Undo, Select All).
Keyboard modifiers should be listed in this order: CMD+CTRL+ALT+SHIFT.