Update documentation for two

Author: sjakobi

Data/HashMap/Internal.hs

@@ -949,14 +949,11 @@ unsafeInsert k0 v0 m0 = runST (go h0 k0 v0 0 m0)
         | otherwise = go h k x s $ BitmapIndexed (mask hy s) (A.singleton t)
 {-# INLINABLE unsafeInsert #-}
 
--- | Create a map from two key-value pairs which hashes don't collide. To
--- enhance sharing, the second key-value pair is represented by the hash of its
--- key and a singleton HashMap pairing its key with its value.
---
--- Note: to avoid silly thunks, this function must be strict in the
--- key. See issue #232. We don't need to force the HashMap argument
--- because it's already in WHNF (having just been matched) and we
--- just put it directly in an array.
+-- | Create a map from a key-value pair and a 'Leaf' or 'Collision' node with
+-- a different hash.
+--
+-- It is the caller's responsibility to ensure that the 'HashMap' argument is
+-- in WHNF.
 two :: Shift -> Hash -> k -> v -> Hash -> HashMap k v -> ST s (HashMap k v)
 two = go
   where