Update README.textile

Added instructions for installing zsh (due to the problems with first time zsh users)
Update README.textile
Update rvm.plugin.zsh

Ruby 2.1.1 -> Ruby 2.1.2.
Merge pull request #2994 from admpsktt/patch-1

Update rvm.plugin.zsh
Merge pull request #2993 from mittalabhas1/master

Update README.textile
Empty commit to close obsolete / solved issues

Please refer to https://github.com/robbyrussell/oh-my-zsh/pull/2983
to see the reason of closing a particular issue.