[upstream-training] Join OpenStack foundation before contribution

Contributors have to join OpenStack Foundation to push codes to gerrit.
Also, the same email address should be used when signing up for
launchpad, gerrit and the foundation.
New contributors often get stuck on these points.

Closes-Bug: #1470454
Change-Id: I9fc747e8113bf83241e60c45f92c94e49eb8171e

doc/upstream-training/source/12-howtocontribute.rst

@@ -13,6 +13,12 @@ http://launchpad.net/
 .. image:: ./_assets/12-01-launchpad-net.png
   :width: 75%
 
+https://www.openstack.org/join/
+===============================
+
+.. image:: ./_assets/12-join-openstack-org.png
+  :width: 100%
+
 http://review.openstack.org
 ===========================
 
@@ -48,6 +54,11 @@ Do you work at a company?
 
 - If your contribution is on behalf of a company, have your managers sign the
   Corporate Contributor License Agreement
+- When signing up for Foundation Membership, make sure to give the same email
+  address you’ll use for code contributions.
+
+  - This will need to match your preferred email address in Gerrit.
+
 - http://docs.openstack.org/infra/manual/developers.html#account-setup
 
 Signed agreement