Every site I build has it's own built in set of documentation. Nothing fancy just a list of quick notes to remind me of the syntax etc.
And the great thing is that Joomla comes with everything you need to create this yourself,
"no addons required!!"
Stage 1 - Use Module Manager in administrator mode
What we are going to do is to create a new administrator module.
This is rarely done so you probably didnt even spot the administrator option in module manager.
Stage 2 - Create a new module
Once we are in Administrator mode we can now create the new module from the toolbar.
Select a New module of the type Custom HTML as this lets us create a simple module that will display any text or images that we want.
Stage 3 - Set the position and order
Once you have entered the text for your Cheat Sheet you must set the module to appear in the "cpanel" position.
If you want it to be always open at the start order it at the very top.
Stage 4 - The final results
Once you have saved and published the module it should look something like this.
Remember that if it is the first module in the cpanel position then it will be "open" by default.
There are some other ways to do this but this is perhaps the easiest and does not require any addons.