Improves module documentation of DynamicSupervisor (#9080)

Fixes #9075

Author: Qqwy

lib/elixir/lib/dynamic_supervisor.ex

@@ -58,7 +58,7 @@ defmodule DynamicSupervisor do
       end
 
   See the `Supervisor` docs for a discussion of when you may want to use
-  module-based supervisors. The `@doc` annotation immediately preceding
+  module-based supervisors. A `@doc` annotation immediately preceding
   `use DynamicSupervisor` will be attached to the generated `child_spec/1`
   function.