Update Wiki/How to install and apply themes for macOS instructions

[tabledrop]

Hello, as I have been using Libresprite on my Mac, I wanted to see any documentation in regards to changing the theme on the macOS version of Libresprite and noticed there was none.

I went ahead to look where the theme/skins folder was located in macOS, and was wondering if this could be added to the specific wiki page regarding themes (after the Linux example):

or macOS:

-- /Applications/libresprite.app/Contents/MacOS/data/skins/ --

-- /path/to/libresprite.app/Contents/MacOS/data/skins/ -- (if installed elsewhere on your system)

Thank you for your consideration!