Bug 1468627 - add docs pointing to ci-admin and ci-configuration; r=tomprince

This is just enough to make these repos discoverable and suggest their usage.
Anything more would duplicate documentation in those repositories.

MozReview-Commit-ID: 1WNEsoQBB9U

--HG--
extra : rebase_source : 19c25ee4b05fe72d2fed37ca68f75db3918d1c2f

taskcluster/docs/actions.rst

@@ -279,7 +279,9 @@ The example below illustrates how to create such an action in Python::
           ...
       },
 
-An equivalent in yaml. Notice that we can't inspect parameters in this case::
+An equivalent in yaml. Notice that we can't inspect parameters in this case:
+
+.. code-block: yaml
 
   ---
   name: retrigger

taskcluster/docs/index.rst

@@ -32,5 +32,6 @@ check out the :doc:`how-to section <how-tos>`.
     actions
     release-promotion
     versioncontrol
+    taskcluster-config
     how-tos
     reference

taskcluster/docs/taskcluster-config.rst

@@ -0,0 +1,35 @@
+Taskcluster Configuration
+=========================
+
+Taskcluster requires configuration of many resources to correctly support Firefox CI.
+Many of those span multiple projects (branches) instead of riding the trains.
+
+Global Settings
+---------------
+
+The data behind configuration of all of these resources is kept in the `ci-configuration`_ repository.
+The files in this repository are intended to be self-documenting, but one of particular interest is ``projects.yml``, which describes the needs of each project.
+
+Configuration Implementation
+----------------------------
+
+Translation of `ci-configuration`_ to Taskcluster resources, and updating those resources, is handled by `ci-admin`_.
+This is a small Python application with commands to generate the expected configuration, compare the expected to actual configuration, and apply the expected configuration.
+Only the ``apply`` subcommand requires elevated privileges.
+
+This tool automatically annotates all managed resources with "DO NOT EDIT", warning users of the administrative UI that changes made through the UI may be reverted.
+
+Changing Configuration
+----------------------
+
+To change Taskcluster configuration, make patches to `ci-configuration`_ or (if necessary) `ci-admin`_, using the Firefox Build System :: Task Configuration Bugzilla component.
+Part of the landing process is for someone with administrative scopes to apply the resulting configuration.
+
+You can test your patches with something like this, assuming ``.`` is a checkout of the `ci-configuration`_ repository containing your changes:
+
+.. code-block: shell
+
+  ci-admin diff --ci-configuration-directory .
+
+.. _ci-configuration: https://hg.mozilla.org/build/ci-configuration/file
+.. _ci-configuration: https://hg.mozilla.org/build/ci-admin/file