Sentinel: document how to undo a renamed command.

sentinel.conf

@@ -230,10 +230,15 @@ sentinel deny-scripts-reconfig yes
 # instead of the normal ones. For example if the master "mymaster", and the
 # associated replicas, have "CONFIG" all renamed to "GUESSME", I could use:
 #
-# sentinel rename-command mymaster CONFIG GUESSME
+# SENTINEL rename-command mymaster CONFIG GUESSME
 #
 # After such configuration is set, every time Sentinel would use CONFIG it will
 # use GUESSME instead. Note that there is no actual need to respect the command
 # case, so writing "config guessme" is the same in the example above.
 #
 # SENTINEL SET can also be used in order to perform this configuration at runtime.
+#
+# In order to set a command back to its original name (undo the renaming), it
+# is possible to just rename a command to itsef:
+#
+# SENTINEL rename-command mymaster CONFIG CONFIG