docs/sock-protocol.txt: update with examples of propagated flag names [#266]

Signed-off-by: Jim Klimov <[email protected]>

Author: jimklimov

docs/sock-protocol.txt

@@ -108,10 +108,14 @@ SETFLAGS
 
 Note that this command takes a variable number of arguments, as multiple
 flags are supported.  Also note that they are not crammed together in
-"", since "RW STRING" would mean something completely different.
+"" quotes, since "RW STRING" would mean something completely different.
 
 This also replaces any previous flags for a given variable.
 
+Currently supported flags include `RW`, `STRING` and `NUMBER`
+(detailed in the NUT Network Protocol documentation); unrecognized values
+are quietly ignored.
+
 ADDCMD
 ~~~~~~