Reference git.o.o DevStack repo rather than GitHub

In docs, use git.o.o URLs rather than GitHub URLs for the DevStack repo,
and don't mention GitHub when git.o.o is more appropriate.
Also, replaced GitHub logo with Git logo in quickstart.png.

Change-Id: Iab0006144f008963b8cb5be2d10ce0f360c0e6ca
diff --git a/doc/source/guides/single-vm.html b/doc/source/guides/single-vm.html
index 2f1990a..d189319 100644
--- a/doc/source/guides/single-vm.html
+++ b/doc/source/guides/single-vm.html
@@ -34,7 +34,7 @@
             <li><a href="../overview.html">Overview</a></li>
             <li><a href="../changes.html">Changes</a></li>
             <li><a href="../faq.html">FAQ</a></li>
-            <li><a href="http://github.com/openstack-dev/devstack">GitHub</a></li>
+            <li><a href="https://git.openstack.org/cgit/openstack-dev/devstack">git.openstack.org</a></li>
             <li><a href="https://review.openstack.org/#/q/status:open+project:openstack-dev/devstack,n,z">Gerrit</a></li>
           </ul>
         </div>
@@ -96,7 +96,7 @@
         DEBIAN_FRONTEND=noninteractive sudo apt-get install -qqy git || sudo yum install -qy git
         sudo chown stack:stack /home/stack
         cd /home/stack
-        git clone https://github.com/openstack-dev/devstack.git
+        git clone https://git.openstack.org/openstack-dev/devstack
         cd devstack
         echo '[[local|localrc]]' > local.conf
         echo ADMIN_PASSWORD=password >> local.conf