Add comment about annotateSet

Author: pete-murphy

recipes/SignalTrisJs/src/Main.purs

@@ -397,6 +397,8 @@ setFillStyleC :: Context2D -> Color -> Effect Unit
 setFillStyleC ctx = setFillStyle ctx <<< toHexString
 
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+-- A faster version of this function is proposed in
+-- https://github.com/purescript/purescript-ordered-collections/issues/50
 annotateSet :: forall a b. Ord a => (a -> b) -> Set a -> Map a b
 annotateSet f = mapWithIndex (\k _ -> f k) <<< toMap