Intructions for QtCreator / msys2

[elliotwoods]

I found that the instructions for setting up Qt Creator on the website are not up to date, and since a lot has changed since that version of Qt Creator, it's very difficult to apply the existing instructions.

I found instead that installing Qt Creator from within msys2 (rather than making it seperately and pointing to it) seems to be a good start rather than setting up everything yourself: https://gist.github.com/bigworld12/c2f2ec25af416f72b6c5f3a9fb4df16f