Starting work on DITA getting started topic

Beginning this as a getting started topic. It will become part of the
planned DITA authoring guide.
Merge remote-tracking branch 'origin/dev' into DITA-guide
Update to first dita topic topic
EXM-24459: New batch validation option in the Validate and Check for Completeness dialog.
First draft of DITA getting started topic.
Edits done while reviewing existing DITA topics.
More edits done while reviewing existing DITA topics.
Remove empty relatable.
Merge branch 'DITA-guide'

* DITA-guide:
  Remove empty relatable.
  More edits done while reviewing existing DITA topics.
  Edits done while reviewing existing DITA topics.
  First draft of DITA getting started topic.
  Update to first dita topic topic
  Starting work on DITA getting started topic

Conflicts:
	DITA/topics/dita-map-validate.dita