Add a target for, and link to, minimal config docs

Reading through the docs for the first time, the reader encounters an
instruction to provide a minimal configuration, with a link that they'd
expect to tell them how to do this.

At present the link actually takes them to the top of
configuration.html, where they read some history about how devstack's
configuration has changed over time.

This is interesting and important and should be in the docs - but in my
opinion a link about setting up a minimal configuration would be more
useful if it takes me to a place that tells them about a minimal
configuration.

To get this, I've had to an an explicit link target into
configuration.rst. I'm not hugely keen on this approach, as I don't
think it scales well. I'd be open to suggestions about other
approaches. The only idea I've had so far though is to simply move the
minimal configuration section right to the top of the page, so that a
link to the doc is a link to the minimal config - the historical
information could be moved to its own topic somewhere further down the doc.

Change-Id: I231ca1b7f17b55f09a4e058dab8ee433893f737e

doc/source/configuration.rst

@@ -95,6 +95,8 @@ Also note that the ``localrc`` section is sourced as a shell script
 fragment and MUST conform to the shell requirements, specifically no
 whitespace around ``=`` (equals).
 
+.. _minimal-configuration:
+
 Minimal Configuration
 =====================
 

doc/source/index.rst

@@ -41,8 +41,7 @@ Quick Start
 
 #. Configure
 
-   We recommend at least a :doc:`minimal
-   configuration <configuration>` be set up.
+   We recommend at least a :ref:`minimal-configuration` be set up.
 
 #. Start the install