Fix typo in README (user->organization)
updating README.md

Adding more instructions for running knife opc on the server itself, to improve clarity
Update readme to mention chef-server-ctl wrapper commands
Update installation directions
Add Chef Server 12 to the description
chef-server-ctl only exists on Chef 12
Add an `opc org edit` command.
Use early exit rather than if-else to improve readability.
Merge pull request #22 from opscode/ssd/add-org-edit

Add an `opc org edit` command.
Added command knife opc user password.

Command either updates the password for a user or, if --enable_external_auth is passed instead of a password, it will enable ldap for that user.