Call out that Int{Set,Map}.size is not O(1) (#1138)

Author: meooow25

containers/src/Data/IntMap/Internal.hs

@@ -575,7 +575,9 @@ null Nil = True
 null _   = False
 {-# INLINE null #-}
 
--- | \(O(n)\). Number of elements in the map.
+-- | \(O(n)\). Number of entries in the map.
+--
+-- __Note__: Unlike @Data.Map.'Data.Map.Lazy.size'@, this is /not/ \(O(1)\).
 --
 -- > size empty                                   == 0
 -- > size (singleton 1 'a')                       == 1

containers/src/Data/IntSet/Internal.hs

@@ -360,6 +360,8 @@ null _   = False
 
 -- | \(O(n)\). Cardinality of the set.
 --
+-- __Note__: Unlike @Data.Set.'Data.Set.size'@, this is /not/ \(O(1)\).
+--
 -- See also: 'compareSize'
 size :: IntSet -> Int
 size = go 0