Update the JIRA Importers Plugin docs to include Redmine Importer docs

Currently https://confluence.atlassian.com/display/JIRA/Migrating+from+Other+Issue+Trackers has information on how to use the JIRA Importers Plugin, however it lists the JIRA Redmine Importer as not being supported here and links to JIM-254 which was resolved on 26/Oct/12 with the creation of the Redmine importer.

The problem is we still list it as being unsupported and have no docs for that plugin, which is actually supported by us. I have raised JIM-860 for the plugin devs to put together some docs, however we need to get those docs and put them on CAC so I have raised this issue.

Can you please update https://confluence.atlassian.com/display/JIRA/Migrating+from+Other+Issue+Trackers as well as JIRA050 and JIRA051 to have these docs? The plugin is available from 5.0.2 to 5.2.

Thanks!