Added gitter badge (handle: mittsu-lemonandroid)

[ghost]

Added a badge for a chat-community on gitter.

You probably want to replace it with your own community, I just made this to showcase how it works.

I intended to start with a chat-community while there is no existing one.

[danini-the-panini]

@LemonAndroid Thanks for your contribution. However, I am going to close this PR for the following reasons:

• I feel the community is small enough that GitHub issues will suffice for now. I would like to see feedback from more community members to see if the addition of gitter is warranted. I suggest creating an issue rather than a PR and hopefully get a discussion going.
• There are a lot more changes here than just the gitter badge. I suggest making individual PRs or Issues with descriptions of the changes/issues in order to invite discussion on them individually.