Update to new CLA process.

CONTRIBUTING.md

@@ -12,25 +12,7 @@ you to do them before we can merge it.
 
 If you plan to contribute in the form of documentation or code, we need you to
 sign our Contributor License Agreement before we can accept your contribution.
-This covers the legalities, confirming that you retain ownership of your
-contributions and that you are licensing them to us.
-
-For some fairly complicated legal reasons we actually have three CLAs.  Which
-of the CLAs you sign depends upon whose behalf you are contributing:
-
-- All individuals (except employees of the U.S. government – see below) should
-  sign the [Individual Contributor License Agreement](http://www.projectcalico.org/community/Individual-Contributor-Agreement).
-- If you are contributing on behalf of a company or organization, *you still
-  need to sign the Individual Contributor License Agreement* as above, but
-  someone at your company or organization also needs to sign the
-  [Corporate Contributor License Agreement](http://www.projectcalico.org/community/corporate-contributor-agreement/)
-  providing a list of people authorized to commit code to Project Calico.
-- Employees of the U.S. government do not sign the Individual Contributor
-  License Agreement.  Instead, someone with authority to sign on behalf of your
-  agency should sign the [U.S Government Contributor License Agreement](http://www.projectcalico.org/community/us-government-contributor-agreement).
-
-It is important to reiterate: until you sign the required agreements we cannot
-accept your contribution!
+You will be prompted to do this as part of the PR process on Github.
 
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