Add missing client doc

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

docs/sources/reference/commandline/cli.rst

@@ -1092,6 +1092,7 @@ containers will not be deleted.
     Remove one or more images
 
       -f, --force=false: Force
+      --no-prune=false: Do not delete untagged parents
 
 Removing tagged images
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