Add docs

Author: andyw8

lib/tapioca/dsl/compilers/devise.rb

@@ -1,11 +1,40 @@
 # typed: true
 # frozen_string_literal: true
 
-require "devise"
+return unless defined?(Devise)
 
 module Tapioca
   module Dsl
     module Compilers
+      # `Tapioca::Dsl::Compilers::Devise` generates RBI files for `ApplicationController``
+      #
+      # For example, with the following routes configuration:
+      #
+      # ~~~rb
+      # Rails.application.routes.draw do
+      #   devise_for :users
+      # end
+      # ~~~
+      #
+      # this compiler will produce the RBI file `user.rbi` with the following content:
+      #
+      # ~~~rbi
+      # # user.rbi
+      # # typed: true
+      # class ApplicationController
+      #   sig { returns(T.nilable(T::Hash[T.untyped, T.untyped])) }
+      #   def user_session; end
+      #
+      #   sig { returns(T::Boolean) }
+      #   def user_signed_in?; end
+      #
+      #   sig { void }
+      #   def authenticate_user!; end
+      #
+      #   sig { returns(T.nilable(User)) }
+      #   def current_user; end
+      # end
+      # ~~~
       class Devise < Tapioca::Dsl::Compiler
         extend T::Sig