docs: update short-help.txt with --quiet-empty flag

doc/short-help.txt

@@ -23,6 +23,8 @@ Options:
           Specify the name to display for a file.
   -d, --diff
           Only show lines that have been added/removed/modified.
+  -E, --quiet-empty
+          Produce no output when the input is empty.
       --tabs <T>
           Set the tab width to T spaces.
       --wrap <mode>