No documentation on how to set up an ouzel project on Mac

[jorgenpt]

The wiki currently only has placeholder content.

[jorgenpt]

Here is a proposed page for instructions on how to set up an ouzel-based project for Mac with Xcode: https://github.com/jorgenpt/ouzel/blob/proposed_wiki_docs/proposed_macos_setup_wiki.markdown

(Sorry for the weird way of proposing the changes, but I don't know of a good way to propose edits to wiki pages on GitHub.)

[elnormous]

This looks really good! I will review it and try to think of a way to allow you to contribute to the documentation.