Fixup typo

src/Options/Applicative.hs

@@ -7,7 +7,7 @@ module Options.Applicative (
   -- See <https://github.com/pcapriotti/optparse-applicative> for a tutorial,
   -- and a general introduction to applicative option parsers.
   --
-  -- See the sections below for more detail
+  -- See the sections below for more detail.
 
   -- * Exported modules
   --
@@ -18,7 +18,7 @@ module Options.Applicative (
   --
   -- | A 'Parser' is the core type in optparse-applicative. A value of type
   -- @Parser a@ represents a specification for a set of options, which will
-  -- yield a value of type a when the command line arguments are successfully
+  -- yield a value of type @a@ when the command line arguments are successfully
   -- parsed.
   --
   -- There are several types of primitive 'Parser'.
@@ -81,7 +81,7 @@ module Options.Applicative (
   -- | 'Parser' builders take a modifier, which represents a modification of the
   -- properties of an option, and can be composed as a monoid.
   --
-  -- Contraints are often used to ensure that the modifiers can be sensibly applied.
+  -- Constraints are often used to ensure that the modifiers can be sensibly applied.
   -- For example, positional arguments can't be specified by long or short names,
   -- so the 'HasName' constraint is used to ensure we have a flag or option.
   Mod,
@@ -115,6 +115,7 @@ module Options.Applicative (
   HasCompleter,
   HasValue,
   HasMetavar,
+
   -- ** Readers
   --
   -- | A reader is used by the 'option' and 'argument' builders to parse