Update installation instructions.

git-svn-id: https://plugins.svn.wordpress.org/polar-polls/trunk@922614 b8457f37-d9ea-0310-8a92-e5e31aec5664
More installation text changes

git-svn-id: https://plugins.svn.wordpress.org/polar-polls/trunk@922620 b8457f37-d9ea-0310-8a92-e5e31aec5664