Added Gitter badge
Update README.md
Merge pull request #29 from gitter-badger/gitter-badge

Add a Gitter chat badge to README.md
There are two links to Gitter.

I removed one of them.
Merge pull request #32 from leehosung/develop

Develop
Merge pull request #33 from leehosung/develop

Add description for a set. This closes #27.
Merge branch 'master' into develop