Add quick overview of do notation in Monad docs

Author: JordanMartinez

src/Control/Monad.purs

@@ -28,6 +28,50 @@ import Data.Unit (Unit)
 -- | - Left Identity: `pure x >>= f = f x`
 -- | - Right Identity: `x >>= pure = x`
 -- | - Applicative Superclass: `apply = ap`
+-- |
+-- | ## Do Notation
+-- |
+-- | When using a type that has an instance for `Monad`, one can use
+-- | "do notation." In short, this code...
+-- | ```
+-- | foo =
+-- |   bind boxedA (\a ->
+-- |     let b = a + 4
+-- |     in bind boxedC (\c ->
+-- |          bind boxedUnit (\_ ->
+-- |            pure (a * b - c)
+-- |          )
+-- |     )
+-- |   )
+-- | ```
+-- |
+-- | ... can be converted into this code...
+-- | ```
+-- | foo =
+-- |   boxedA >>= (\a ->
+-- |     let b = a + 4
+-- |     in boxedC >>= (\c ->
+-- |          boxedUnit >>= (\_ ->
+-- |            pure (a * b - c)
+-- |          )
+-- |     )
+-- |   )
+-- | ```
+-- |
+-- | ...which can be converted once more into "do notation:"
+-- | ```
+-- | foo = do
+-- |   a <- boxedA
+-- |   let b = a + 4
+-- |   c <- boxedC
+-- |   boxedUnit
+-- |   pure (a * b - c)
+-- | ```
+-- |
+-- | Note: if one wants to use "do notation" but redefine what the in-scope
+-- | definitions are for `bind` and `pure` in a given context, one can use
+-- | "qualified do notation." This is an intermediate/advanced language feature
+-- | not explained here.
 class (Applicative m, Bind m) <= Monad m
 
 instance monadFn :: Monad ((->) r)