dillon1000/react

Updated CONTRIBUTING.md: Mention of "facebook.com" was not a link

Updated the mention of "facebook.com" on line 3 of the CONTRIBUTING.md file to link to Facebook. Previously, this mention was just in plain text.

Changed from `facebook.com` to `[facebook.com](https://facebook.com)`

No other content has been changed. Content has not been removed from this file in any way.