Remove redundant target in README

An 'example' anchor was being explicitly added that was
redundant with the 'Example' title it preceeded. This
causes failures with `python setup.py check -s -r` which
was added to release validation to prevent pypi package
upload failures.

Since the README is imported into the built docs, and the
docs link to the examples using this hidden anchor, this
renames it to avoid a conflict.

Change-Id: I6947e0ae420402cc9866e3c374626392b1d5194c
(cherry picked from commit df4c5819d2)

README.rst

@@ -17,7 +17,7 @@ library, and adding logic and features that the OpenStack Infra team had
 developed to run client applications at scale, it turned out that we'd written
 nine-tenths of what we'd need to have a standalone library.
 
-.. _example:
+.. _usage_example:
 
 Example
 =======

doc/source/user/usage.rst

@@ -6,7 +6,7 @@ To use shade in a project::
 
 	import shade
 
-For a simple example, see :ref:`example`.
+For a simple example, see :ref:`usage_example`.
 
 .. note::
   API methods that return a description of an OpenStack resource (e.g.,