Add example of change log.

CHANGES.rst

+This is a running log of changes to libvmod-example.
+
+libvmod-example 0.2 (unreleased)
+--------------------------------
+
+* The most recent release entry is at the top.
+
+libvmod-example 0.1 (1970-01-01)
+--------------------------------
+
+* Add list items with changes done.
+* Issues fixed could also be list entries.
+
+If you need to, a paragraph or two of explanation for any complicated changes
+is appreciated.
+
+Make sure to mention any changing breaking user-visible interfaces. (function
+names, type of arguments, order of arguments)
+
+