CONTRIBUTING.md: remove stale text

Remove some now-stale and redundant text.  This probably could have
been done in bf52156, but was missed.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres

.github/CONTRIBUTING.md

@@ -5,14 +5,7 @@ Open MPI!
 
 ![You're awesome!](https://www.open-mpi.org/images/youre-awesome.jpg)
 
-General information about contributing to the Open MPI project can be
-found at the [Contributing to Open MPI
-webpage](https://docs.open-mpi.org/en/main/contributing.html).
-
-In short: Open MPI is hosted on GitHub, and we gladly accept pull
-requests.  The instructions below are specifically for opening issues
-and pull requests against Open MPI.
-
+Open MPI is hosted on GitHub, and we gladly accept pull requests.
 Please see the [Contributing
 guidelines](https://docs.open-mpi.org/en/main/contributing.html) for
-more details on how to contribute to Open MPI.
+details on how to contribute to Open MPI.