Document change.move config parameter
Document change.move config parameter

This config parameter allows to disable the Move Change REST endpoint.
It was added in change I26466e359 and was meant as a temporary measure
until we decide how to solve the issues with the move change
functionality (in particular issue 9877). However so far we didn't
follow up on this, hence we should better document this setting while
it's there and being used.

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: I4194c55800c4ef5c48b2ffc9bd6988baedcba89c

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