Update the workflow document to talk about renaming transitions that came from the default worklow

The defrault worklow has "jira.i18n.title" and "jira.i18n.description" properties for its transitions. This is done so that the transitions can be translated. However, if the workflow is copied, and transitions are simply renamed, it does not work, until the proeprties are removed.

I believe the JIRA Workflow Editor, does warn users about this, but I think we need to also mention this in the docs.

See JRA-14453 for an example of where this caused confusion.