[docs] Expand a bit on the basics of a buildbot policy

We don't have much publicly documented about how build bots are maintained, and who has what responsibility with regards to the bots themselves and failures they report.

This change adds some basic framing on the topic. It is intended to simplify document long standing practice, and to avoid introducing any new policy elements. I do want to propose a couple of changes, but those will happen with their own review and broader discussion.

Differential Revision: https://reviews.llvm.org/D112755

llvm/docs/HowToAddABuilder.rst

@@ -13,12 +13,41 @@ Buildmasters
 
 There are two buildmasters running.
 
-* The main buildmaster at `<https://lab.llvm.org/buildbot>`_. All builders attached
-  to this machine will notify commit authors every time they break the build.
-* The staging buildbot at `<https://lab.llvm.org/staging>`_. All builders attached
-  to this machine will be completely silent by default when the build is broken.
-  Builders for experimental backends should generally be attached to this
-  buildmaster.
+* The main buildmaster at `<https://lab.llvm.org/buildbot>`_. All builders
+  attached to this machine will notify commit authors every time they break
+  the build.
+* The staging buildmaster at `<https://lab.llvm.org/staging>`_. All builders
+  attached to this machine will be completely silent by default when the build
+  is broken.
+
+In order to remain connected to the main buildmaster (and thus notify
+developers of failures), a builbot must:
+
+* Be building a supported configuration.  Builders for experimental backends
+  should generally be attached to staging buildmaster.
+* Be able to keep up with new commits to the main branch, or at a minimum
+  recover to tip of tree within a couple of days of falling behind.
+
+Additionally, we encourage all bot owners to point their bots towards the
+staging master during maintenance windows, instability troubleshooting, and
+such.
+
+Roles & Expectations
+====================
+
+Each buildbot has an owner who is the responsible party for addressing problems
+which arise with said buildbot.  We generally expect the bot owner to be
+reasonably responsive.
+
+For some bots, the ownership responsibility is split between a "resource owner"
+who provides the underlying machine resource, and a "configuration owner" who
+maintains the build configuration.  Generally, operational responsibility lies
+with the "config owner".  We do expect "resource owners" - who are generally
+the contact listed in a workers attributes - to proxy requests to the relevant
+"config owner" in a timely manner.
+
+Most issues with a buildbot should be addressed directly with a bot owner
+via email.  Please CC `Galina Kistanova <mailto:gkistanova@gmail.com>`_.
 
 Steps To Add Builder To LLVM Buildbot
 =====================================