Create RenPy.gitignore

[kath-hill]

This is an extended version of the Python .gitignore file and doesn't include cached files, navigation files, or other files that should not be included in a production version of a Ren'Py project.

Reasons for making this change

Developers of Ren'Py games should have a pre-made template so they don't have to write it all themselves.

If this is a new template

Link to application or project’s homepage: https://github.com/kath-hill/PDL/