Add docs for Chocolatey GUI file locations

It would be good to add some documentation for the location of the files that Chocolatey GUI uses.

Some known files:

* `C:\ProgramData\Chocolatey GUI\Config\data.db`
* `C:\Users\\AppData\Local\Chocolatey GUI\data.db`
* `C:\Users\\AppData\Local\Chocolatey\ChocolateyGui.exe_StrongName_qgbusv5dfgkxx33orw4dqzgj3f5c3jne\0.19.0.0\user.config`
* `C:\Users\\Appdata\Local\Chocolatey GUI\outdatedPackages.xml`

📓 NOTE: This is currently an issue created to track that we want to do this. I will come back to it to flesh out some of the locations that I'm aware of.