Remove OS X Support from Readme

This commit removes the notation in the Readme that OS X is supported.
Merge pull request #15 from sbonami/13-Temporarily-remove-support-for-OS-X

Remove OS X Support from Readme
Merge branch 'master' of https://github.com/sbonami/PFIncrementalStore into 14-Add-OS-X-Support

* 'master' of https://github.com/sbonami/PFIncrementalStore:
  Remove OS X Support from Readme
Revert "Remove OS X Support from Readme"

This reverts commit 3ea3124481fa23acadd7b1c50cab2a26d655f04b.