Recommend --data-binary flag when testing submit rules from curl

Change-Id: I446750051f9f8be7fdd8ef7a93307303c6746a2d
(cherry picked from commit b42e303d38)

Documentation/rest-api-changes.txt

@@ -2574,6 +2574,17 @@ describing the permutations that satisfy the tested submit rule.
   ]
 ----
 
+When testing with the `curl` command line client the
+`--data-binary @rules.pl` flag should be used to ensure
+all LFs are included in the Prolog code:
+
+----
+  curl -X POST \
+    -H 'Content-Type: text/plain; charset=UTF-8' \
+    --data-binary @rules.pl \
+    http://.../test.submit_rule
+----
+
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