Add mustache.vim repository

[Marian Schubert]

mustache.vim is a simple plugin for working with mustache templates. It has both syntax hilighting and indenting, which just borrows from html indent plugin.

https://github.com/juvenn/mustache.vim

[ZyX_I]

It is not present on vim.org, isn’t it?

I created [my own commit](https://github.com/MarcWeber/vim-addon-manager-known-repositories/commit/6e732f2f4a29df5aa269c143dcb6e6e614caf874) because in your one repository url is “https://”, while in other it is “git:”.