Added a note for ap

We've got this pr like 4 times now thinking that it's a typo.

Author: hemanth

readme.md

@@ -349,7 +349,7 @@ Lifting is when you take a value and put it into an object like a [functor](#poi
 Some implementations have a function called `lift`, or `liftA2` to make it easier to run functions on functors.
 
 ```js
-const liftA2 = (f) => (a, b) => a.map(f).ap(b)
+const liftA2 = (f) => (a, b) => a.map(f).ap(b) // note it's `ap` and not `map`.
 
 const mult = a => b => a * b