Update document of 'Move Change' REST endpoint
Update document of 'Move Change' REST endpoint

This change updates the 'Move Change' doc to notice users
the difference between this endpoint and the cherry-pick
endpoint.

Change-Id: Ibf29e4493d1d1c962cc7e45c9526f9317957efc5

gerrit-review/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,gerrit-review/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,gerrit-review/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,gerrit-review/gerrit,gerrit-review/gerrit,WANdisco/gerrit,gerrit-review/gerrit,WANdisco/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,gerrit-review/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit