Add 5.2 and 6.0 to documentation list.

Also remove a trailing whitespace that was screaming at me.

R1/source/docs/index.rst

@@ -10,6 +10,10 @@ We're trying to keep the official documentation in sync with the code.
 Both are kept in same source repository and both are available online:
 
 -  `Documentation for the latest release
+   6.0 <https://www.varnish-cache.org/docs/6.0/>`__
+-  `Documentation for
+   5.2 <https://www.varnish-cache.org/docs/5.2/>`__
+-  `Documentation for
    5.1 <https://www.varnish-cache.org/docs/5.1/>`__
 -  `Documentation for
    5.0 <https://www.varnish-cache.org/docs/5.0/>`__