Added codeclimate badge to readme

[iainbeeston]

I think code climate might be useful.

I did try setting up code coverage in code climate as well (ie. make the travis build run simplecov, push the results to code climate and then code climate shows you coverage statistics along side code metrics) but I believe only the owner of the repo can do that (in code climate)

[iainbeeston]

@hoxworth If you'd like to set up code coverage as well, I'll need you to go to the code climate page for the project (through the link in the readme) go to settings, and encode the CODECLIMATE_REPO_TOKEN for Travis (eg. "travis encrypt CODECLIMATE_REPO_TOKEN=secret" if you have the travis gem installed) and post it back here, then I can do the rest

[pd]

@iainbeeston I tried this morning to get simplecov to work, but couldn't get it to actually track coverage of the test run. Have you managed to get an accurate coverage report out of anything yet?

What I tried:

1. Update all tests to just start with require_relative 'test_helper'
2. Add the usual require 'simplecov'; SimpleCov.start to the top of test_helper, then require json-schema
3. Run with rake or ruby test/test_some_particular_test.rb.

For reasons I couldn't grok, tho, SimpleCov would generate the coverage report before any tests actually ran -- so I could see the whole library loaded, but most everything was reported as uncovered.

[iainbeeston]

I haven't tried it on json-schema. But I did set it up for one of my own
gems, or rather, I set up code coverage with code climate (
https://github.com/iainbeeston/nickel) which uses simplecov underneath (I
believe)