Fixed missing init.lua warning

Related: #4

The documentation now provides a better recommendation for running this action in a Neovim configuration to avoid warnings such as:

 Configuration ~
- WARNING Missing user config file: /Users/runner/.config/nvim/init.lua
  - ADVICE:
    - :help |config|

Added Better Plugin Support

It should be possible to use this action with Neovim plugins now. See nvim-best-practices-plugin-template for details

Initial Release

Checked that this works on a basic Neovim configuration and plugin. It also checks for deprecation notices on Neovim nightly automatically. Neat!