[docs] Update new builder instructions to starting on the staging buildmaster

[reames]

Summary

This adds a step in the instructions to switch to the production buildmaster at the very end (after explicit approval), and updates the early instruction to start with the builder pointed at the staging buildmaster.

[gkistanova]

Thanks, Philip!
LGTM.

llvm/docs/HowToAddABuilder.rst

 #. Create a designated user account, your buildbot-worker will be running under,
    and set appropriate permissions.
 
 #. Choose the buildbot-worker root directory (all builds will be placed under
    it), buildbot-worker access name and password the build master will be using
    to authenticate your buildbot-worker.
 
 #. Create a buildbot-worker in context of that buildbot-worker account. Point it
-   to the **lab.llvm.org** port **9990** (see `Buildbot documentation,
+   to the **lab.llvm.org** port **9994** (see `Buildbot documentation,
    Creating a worker
    <http://docs.buildbot.net/current/tutorial/firstrun.html#creating-a-worker>`_
    for more details) by running the following command:
 
     .. code-block:: bash
 
        $ buildbot-worker create-worker <buildbot-worker-root-directory> \
-                    lab.llvm.org:9990 \
+                    lab.llvm.org:9994 \
                     <buildbot-worker-access-name> \
                     <buildbot-worker-access-password>
 
-   To point a worker to silent master please use lab.llvm.org:9994 instead
-   of lab.llvm.org:9990.
+   This will cause your new worker to connect to the staging buildmaster
+   which is silent by default.  Only once a new worker is stable, and
+   approval from Galina has been received (see last step) should it
+   be pointed at the main buildmaster.
 
 #. Fill the buildbot-worker description and admin name/e-mail.  Here is an
    example of the buildbot-worker description::
 
        Windows 7 x64
        Core i7 (2.66GHz), 16GB of RAM
 
        g++.exe (TDM-1 mingw32) 4.4.0
#. Send a patch which adds your build worker and your builder to
    This is particularly useful for the staging buildmaster which is silent
    otherwise.
 
 #. Send the buildbot-worker access name and the access password directly to
    `Galina Kistanova <mailto:[e-mail]>`_, and wait till she
    will let you know that your changes are applied and buildmaster is
    reconfigured.
 
-#. Check the status of your buildbot-worker on the `Waterfall Display
-   <http://lab.llvm.org/buildbot/#/waterfall>`_ to make sure it is connected,
-   and the `Workers Display <http://lab.llvm.org/buildbot/#/workers>`_ to see if
-   administrator contact and worker information are correct.
-
-#. Wait for the first build to succeed and enjoy.
-
+#. Check the status of your buildbot-worker on the `Waterfall Display (Staging)
+   <http://lab.llvm.org/staging/#/waterfall>`_ to make sure it is
+   connected, and the `Workers Display (Staging)
+   <http://lab.llvm.org/staging/#/workers>`_ to see if administrator
+   contact and worker information are correct.
+
+#. At this point, you have a working builder connected to the staging
+   buildmaster.  You can now make sure it is reliably green and keeps
+   up with the build queue.  No notifications will be sent, so you can
+   keep an unstable builder connected to staging indefinitely.
+
+#. (Optional) Once the builder is stable on the staging buildmaster with
+   several days of green history, you can chose to move it to the production
+   buildmaster to enable developer notifications.  Please email `Galina
+   Kistanova <mailto:[e-mail]>`_ for review and approval.
+
+   To move a worker to production (once approved), stop your worker, edit the
+   buildbot.tac file to change the port number from 9994 to 9990 and start it
+   again.
 
 Best Practices for Configuring a Fast Builder
 =============================================
 
 As mentioned above, we generally have a strong preference for
 builders which can build every commit as they come in.  This section
 includes best practices and some recommendations as to how to achieve
 that end.