Add a Gitter chat badge to README.md

[gitter-badger]

ShitLib/shitlib-java now has a Chat Room on Gitter

@artemisia-absynthium has just created a chat room. You can visit it here: https://gitter.im/ShitLib/shitlib-java.

This pull-request adds this badge to your README.md:

If my aim is a little off, please let me know.

Happy chatting.

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[codecov]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             master     #3   +/-   ##
=======================================
  Coverage       100%   100%           
- Complexity        0      7    +7     
=======================================
  Files             1      1           
  Lines             7      7           
=======================================
  Hits              7      7

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