Folding is undocumented

[fancsali]

As the title suggests; I found out there's folding by browsing the code. It would be nice, if the documentation would also mention it.

[tpope]

Documentation is now upstream: https://github.com/vim/vim/blob/f4fcedc59d4cc5ae6b5270a933e8377030283c1c/runtime/doc/filetype.txt#L632-L635

[anthony-geoghegan]

I only just realised that folding is provided by this plugin and after a few experiments, I was about to suggest a pull request to add the same documentation to this project’s README. Then I remembered that #135 includes various improvements for the README – and this is one of them.