The Sumneko Lua language server has matured quite a bit and many
Neovim developers use it while working on Neovim. Having a default
configuration for Neovim development is a nice convenience (and
dovetails well with the auto-generated compile_command.json for C
development).
The file is shipped under `contrib` and users can make use of it by
symlinking to `.luarc.json` in the project root.
