Additional help messaging to help the user resolve a conflicted migration

Added additional help messaging for command line scaffold generation. When a migration already exists for the resource, the user is now alerted that they are able to skip the conflicted migration file via the --skip option.

This functionality already exists; I've just updated the help output to remind the user that skipping the migration creation is an option as well.
@arthurnn Good idea.  I've made a modification to eliminate the string concatenation.