Add Coveralls Community Backend

[merijnS]

No description provided.

[coveralls]

Coverage increased (+0.0008%) to 97.005% when pulling 32dfe97 on Groninger-Bugbusters:master into a4f099e on chaoss:master.

[vchrombie]

Thanks for the PR @merijnS. We love to see our contributors come up with more data sources. Thinking about it, Coveralls is an excellent data source and I must appreciate your team @Groninger-Bugbusters have done awesome work.

I have some questions though. Is the backend ready to use? I see that the backend needs a repo URL as an argument but I couldn't see any information regarding it in the readme file.

Also, it would be great if you can fix the issue with the sign-off.

$ git commit --amend -s
$ git push -f origin master

You can also edit the commit message during this time. https://github.com/chaoss/grimoirelab/blob/master/CONTRIBUTING.md#guidelines-to-follow-to-write-good-commit-messages

It can be something like (you can add more details according to the guidelines)

[docs] Add Coveralls Community Backend

This commit adds the coveralls backend repository link to the 
Community Backends section in the README.md file.

<<sign-off string>>

Please let me know if you need any help.

[merijnS]

Thanks for the info @vchrombie! I have updated the commit.