[llvm][Docs] Expand MyFirstTypoFix's post-commit section (#79827)

And link to it from the GitHub guide. Since it fits in the flow of the
former document better, but is of interest to those using the GitHub
specific guide.

This includes some content I wrote for an automated PR comment but I
think is useful to have in a single place to link to instead.

I have removed some details:
* About the waterfall view because it doesn't seem that useful to new
contributors and is likely to just seem like constant chaos given how
many builds are going on.
* The orange bubbles in the console view. I also remember this being the
case but whether it was changed, or the web UI is just not loading
properly, I now see red builds that were red before that commit. So
again, it seems like detail that's not needed for a new contributor.

Author: DavidSpickett

llvm/docs/GitHub.rst

@@ -170,6 +170,17 @@ request will understand that you're rebasing just your patches, and display
 this result correctly with a note that a force push did occur.
 
 
+Problems After Landing Your Change
+==================================
+
+Even though your PR passed the pre-commit checks and is approved by reviewers, it
+may cause problems for some configurations after it lands. You will be notified
+if this happens and the community is ready to help you fix the problems.
+
+This process is described in detail
+:ref:`here <MyFirstTypoFix Issues After Landing Your PR>`.
+
+
 Checking out another PR locally
 -------------------------------
 Sometimes you want to review another person's PR on your local machine to run

llvm/docs/MyFirstTypoFix.rst

@@ -448,37 +448,44 @@ Actually, this would be a great time to read the rest of the :ref:`developer
 policy <developer_policy>` too.
 
 
-Post-commit errors
-==================
+.. _MyFirstTypoFix Issues After Landing Your PR:
+
+Issues After Landing Your PR
+============================
 
 Once your change is submitted it will be picked up by automated build
 bots that will build and test your patch in a variety of configurations.
 
-You can see all configurations and their current state in a waterfall
-view at http://lab.llvm.org/buildbot/#/waterfall. The waterfall view is good
-to get a general overview over the tested configurations and to see
-which configuration have been broken for a while.
+The "console" view at http://lab.llvm.org/buildbot/#/console displays results
+for specific commits. If you want to follow how your change is affecting the
+build bots, this should be the first place to look.
+
+The columns are build configurations and the rows are individual commits. Along
+the rows are colored bubbles. The color of the bubble represents the build's
+status. Green is passing, red has failed and yellow is a build in progress.
+
+A red build may have already been failing before your change was committed. This
+means you didn't break the build but you should check that you did not make it
+any worse by adding new problems.
 
-The console view at http://lab.llvm.org/buildbot/#/console helps to get a
-better understanding of the build results of a specific patch. If you
-want to follow along how your change is affecting the build bots, **this
-should be the first place to look at**.
+.. note::
+   Only recent changes are shown in the console view. If your change is not
+   there, rely on PR comments and build bot emails to notify you of any problems.
 
-Note: only recent changes are shown in the console view. So if your change
-is not there, please rely on PR comments and buildbot emails to notify you
-of any issues intead.
+If there is a problem in a build that includes your changes, you may receive
+a report by email or as a comment on your PR. Please check whether the problem
+has been caused by your changes specifically. As builds contain changes from
+many authors and sometimes fail due to unrelated infrastructure problems.
 
-The colored bubbles correspond to projects in the waterfall. If you see a broken
-build, do not despair - some build bots are
-continuously broken; if your change broke the build, you will see a red
-bubble in the console view, while an already broken build will show an
-orange bubble. Of course, even when the build was already broken, a new
-change might introduce a hidden new failure.
+To see the details of a build, click the bubble in the console view, or the link
+provided in the problem report. You will be able to view and download logs for
+each stage of that build.
 
-When you want to see more details how a specific build is broken, click the red bubble.
-If the error logs confuse you, do not worry - you can ask for help by adding a comment
-to your PR, or asking on `Discord <https://discord.com/invite/xS7Z362>`__.
+If you need help understanding the problem, or have any other questions, you can
+ask them as a comment on your PR, or on `Discord <https://discord.com/invite/xS7Z362>`__.
 
+If you do not receive any reports of problems, no action is required from you.
+Your changes are working as expected, well done!
 
 Reverts
 -------