README.md: Update playbook invocation for ansible become

See: https://docs.ansible.com/ansible/become.html

Signed-off-by: Alan Orth <alan.orth@gmail.com>

README.md

@@ -17,7 +17,7 @@ web01
 ## Use
 Once you've satisfied the the above assumptions, you can execute:
 
-    $ ansible-playbook web.yml -i hosts -K
+    $ ansible-playbook web.yml -i hosts --ask-become-pass
 
 ## License
 Copyright (C) 2014 - 2015 Alan Orth