update installation section of readme

git-svn-id: https://plugins.svn.wordpress.org/huzzaz-video-gallery/trunk@774034 b8457f37-d9ea-0310-8a92-e5e31aec5664
update installation section of readme

git-svn-id: https://plugins.svn.wordpress.org/huzzaz-video-gallery/trunk@774035 b8457f37-d9ea-0310-8a92-e5e31aec5664