Update docs encouraging the use of before over nilM

core/src/Streamly/Internal/Data/Stream/Exception.hs

@@ -180,7 +180,6 @@ gbracket bef aft onExc onGC ftry action =
 --
 -- Same as the following but more efficient due to fusion:
 --
--- >>> before action xs = Stream.nilM action <> xs
 -- >>> before action xs = Stream.concatMap (const xs) (Stream.fromEffect action)
 --
 {-# INLINE_NORMAL before #-}

core/src/Streamly/Internal/Data/Stream/Type.hs

@@ -225,6 +225,7 @@ pattern Stream step state <- (unShare -> UnStream step state)
 -- | A stream that terminates without producing any output, but produces a side
 -- effect.
 --
+-- >>> nilM action = Stream.before action Stream.nil
 -- >>> Stream.fold Fold.toList (Stream.nilM (print "nil"))
 -- "nil"
 -- []