Issue#57:
Add certificate (public key) in Stub App_Data.
Add a link to allow download of it.
Added info about contriburs.txt file to contribution guide.
Explain a bit more about the certificate link
Merge pull request #93 from arieltrevisan/issue-57

Add link to download public certificate for SPs to validate SAML responses.
Fixes #57.
Commiting automatically changed _reference.js.
- This file keeps being changed automatically over and over again. Checking in this version and hoping that it will stop bothering me again.