[docs] Referenced llvm workflow in HowToAddABuilder

[gkistanova]

Thanks for adding this, Mircea!
Recently this became an issue, as people started using github PRs as a way to propose patches.

llvm/docs/HowToAddABuilder.rst

example of the buildslave description::
        Microsoft(R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86
 
 #. Make sure you can actually start the buildslave successfully. Then set
    up your buildslave to start automatically at the start up time.  See the
    buildbot documentation for help.  You may want to restart your computer
    to see if it works.
 
 #. Send a patch which adds your build slave and your builder to
-   `zorg <https://github.com/llvm/llvm-zorg>`_.
+   `zorg <https://github.com/llvm/llvm-zorg>`_. Use the typical LLVM 
+   `workflow <https://llvm.org/docs/Contributing.html#how-to-submit-a-patch>`_.
 
    * slaves are added to ``buildbot/osuosl/master/config/slaves.py``
    * builders are added to ``buildbot/osuosl/master/config/builders.py``
 
    Please make sure your builder name and its builddir are unique through the
    file.
 
    It is possible to whitelist email addresses to unconditionally receive