Improved docs & change log section on README page
Improved docs & change log section on README page

Details:

* Simplified the links to documentation by removing the links to the
  development master branch, because that is just confusing to users
  and for docs build success we have the docs button at the top of the
  page.

* Added link to change log of latest released version.

Signed-off-by: Andreas Maier <38dbb04957d222ea6ce72de72413b1e55e665472@de.ibm.com>

zhmcclient/python-zhmcclient,zhmcclient/python-zhmcclient