Bug 1415619: Add some sphinx documentation pointing at taskgraph configuration. r=dustin

MozReview-Commit-ID: 3EAu9bkln8h

--HG--
extra : rebase_source : 0acb6c32a3a1a4bec24513006a586e9a422e1728

taskcluster/docs/taskgraph.rst

@@ -169,6 +169,15 @@ using simple parameterized values, as follows:
     Multiple labels may be substituted in a single string, and ``<<>`` can be
     used to escape a literal ``<``.
 
+Graph Configuration
+-------------------
+
+There are several configuration settings that are pertain to the entire
+taskgraph. These are specified in :file:`config.yml` at the root of the
+taskgraph configuration (typically :file:`taskcluster/ci`). The available
+settings are documented inline in `taskcluster/taskgraph/config.py
+<https://dxr.mozilla.org/mozilla-central/source/taskcluster/taskgraph/config.py>`_.
+
 .. _taskgraph-trust-domain:
 
 Trust Domain