Godot addon GitIgnore for submodule support

.gitignore

#
# This Git Ignore file is intended for use with developing Godot Addons. 
# Ideally this will be in a separate release branch that can be added as a submodule through git
# The purpose of this is that addons actively being developed on GitHub can be readily 
# updated, tested, and reverted to older commits as needed for the particular project.
# Obviously this is an opt-in thing. But it could make godot addons much easier to use for more involved projects.
#
# For all who choose to follow this paradigm, the recommended branch name is `submod-addon`.
#
# For those less familiar with Git, you can learn more about submodules here: https://git-scm.com/book/en/v2/Git-Tools-Submodules
# 
# How this works is by merging into the `submod-addon` branch, anything outside of your addons folder 
# is stripped and only the addon itself is included. This means you can have as much or as little testing 
# systems outside in the main project folders
# 
# Another recommendation for this would be to place a copy of your README and LICENSE files into the addon folder, 
# specifically the folder for your addon. This makes it easier to find your resources and how you allow the addon to be used
# when the addon has been installed as a submodule.
#

# changes from block-list to include list via blocking everything, then `!` includes a specific pattern or file
*
!*/

# track this file
!.gitignore

# whitelist everything in ./addons/
!addons/

Note: changing to !addons/** better supports tracking all subfiles