Adding inside bottom option to `np_pos`

git-svn-id: https://plugins.svn.wordpress.org/rotatingtweets/trunk@939883 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updating readme.txt to reflect new option

git-svn-id: https://plugins.svn.wordpress.org/rotatingtweets/trunk@939884 b8457f37-d9ea-0310-8a92-e5e31aec5664