add missing doc

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)

docs/sources/reference/commandline/cli.rst

@@ -1023,6 +1023,8 @@ containers will not be deleted.
     Usage: docker rmi IMAGE [IMAGE...]
 
     Remove one or more images
+
+      -f, --force=false: Force
     
 Removing tagged images
 ~~~~~~~~~~~~~~~~~~~~~~