cli: Document use of -a <app> in 'remote add'
cli: Document use of -a <app> in 'remote add'

Fixes #2404.

Signed-off-by: Philip Lehmann-Boehm <3ba3974e96044dcde818e6310ed799abe10671d4@philiplb.de>
philiplb/flynn,flynn/flynn,flynn/flynn,lmars/flynn,flynn/flynn,lmars/flynn,philiplb/flynn,flynn/flynn,lmars/flynn,philiplb/flynn,lmars/flynn,flynn/flynn,philiplb/flynn,philiplb/flynn,lmars/flynn