[docs] Update PTL info in contributor guide

Some recent emails have made me realize that the basic contributor
doc doesn't have info about where you can find out who the current
PTL is.  This patch moves the PTL info from the bottom of the doc
to a more visible place, and adds a brief description of what the
PTL does and who the electorate is.

Change-Id: Ib1fe4fba3d4911222b2c9393700c411d08fe2805

doc/source/contributor/contributing.rst

@@ -164,6 +164,33 @@ https://review.opendev.org/#/admin/groups/83,members
 You can also find the members of the cinder-core team at the Cinder weekly
 meetings.
 
+Project Team Lead
+~~~~~~~~~~~~~~~~~
+
+For each development cycle, Cinder project Active Technical Contributors (ATCs)
+elect a Project Team Lead who is responsible for running the weekly meetings,
+midcycles, and Cinder sessions at the Project Team Gathering for that cycle
+(and who is also ultimately responsible for everything else the project does).
+
+* You automatically become an ATC by making a commit to one of the cinder
+  deliverables.  Other people who haven't made a commit, but have contributed
+  to the project in other ways (for example, making good bug reports) may be
+  recognized as "extra-ATCs" and obtain voting privileges.  If you are such
+  a person, contact the current PTL before the "Extra-ATC freeze" indicated
+  on the current development cycle schedule (which you can find from the
+  `OpenStack Releases homepage
+  <https://releases.openstack.org/index.html>`_ .
+
+The current Cinder project Project Team Lead (PTL) is listed in the
+`Cinder project reference
+<https://governance.openstack.org/tc/reference/projects/cinder.html>`_
+maintained by the OpenStack Technical Committee.
+
+All common PTL duties are enumerated in the `PTL guide
+<https://docs.openstack.org/project-team-guide/ptl.html>`_.
+
+Additional responsibilities for the Cinder PTL can be found by reading through
+the :ref:`managing-development` section of the Cinder documentation.
 
 New Feature Planning
 ~~~~~~~~~~~~~~~~~~~~
@@ -315,12 +342,3 @@ from https://releases.openstack.org/
 
 You can see who's been doing what with Cinder recently in Stackalytics:
 https://www.stackalytics.io/report/activity?module=cinder-group
-
-Project Team Lead Duties
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-All common PTL duties are enumerated in the `PTL guide
-<https://docs.openstack.org/project-team-guide/ptl.html>`_.
-
-Additional responsibilities for the Cinder PTL can be found by reading through
-the :ref:`managing-development` section of the Cinder documentation.