Updates to multiple salt-ssh/roster docs.

Updated the salt-ssh.rst to add the new options that are available via the command line. Modified the ssh index.rst to include a link to the salt-ssh cli commands page. Updated parsers.py to fix the default value that is present in the documentation from 5 to 25 (as 25 is the actual default). Updated roster.rst to note that the default file location is /etc/salt/roster since it was absent, and might be confusing if you head to the roster documentation before reading the rest of the salt-ssh documentation.