Include READMEs in main framework pages of the API documentation

Currently when opening the main framework pages there is no introduction
to the framework. Instead we only see a whole lot of modules and the
`gem_version` and `version` methods.

By including the READMEs using the `:include:` directive each frameworks
has a nice introduction.
For markdown READMEs we need to add the :markup: directive.

[ci-skip]

Co-authored-by: zzak <zzakscott@gmail.com>

actioncable/lib/action_cable.rb

@@ -43,6 +43,8 @@
   loader.inflector.inflect("postgresql" => "PostgreSQL")
 end.setup
 
+# :markup: markdown
+# :include: actioncable/README.md
 module ActionCable
   require_relative "action_cable/version"
   require_relative "action_cable/deprecator"

actionmailbox/lib/action_mailbox.rb

@@ -8,6 +8,8 @@
 require "action_mailbox/deprecator"
 require "action_mailbox/mail_ext"
 
+# :markup: markdown
+# :include: actionmailbox/README.md
 module ActionMailbox
   extend ActiveSupport::Autoload
 

actionmailer/lib/action_mailer.rb

@@ -35,6 +35,7 @@
 require "active_support/core_ext/string/inflections"
 require "active_support/lazy_load_hooks"
 
+# :include: actionmailer/README.rdoc
 module ActionMailer
   extend ::ActiveSupport::Autoload
 

actiontext/lib/action_text.rb

@@ -8,6 +8,8 @@
 
 require "nokogiri"
 
+# :markup: markdown
+# :include: actiontext/README.md
 module ActionText
   extend ActiveSupport::Autoload
 

actionview/lib/action_view.rb

@@ -28,6 +28,7 @@
 require "action_view/version"
 require "action_view/deprecator"
 
+# :include: actionview/README.rdoc
 module ActionView
   extend ActiveSupport::Autoload
 

activejob/lib/active_job.rb

@@ -29,6 +29,8 @@
 require "active_job/deprecator"
 require "global_id"
 
+# :markup: markdown
+# :include: activejob/README.md
 module ActiveJob
   extend ActiveSupport::Autoload
 

activemodel/lib/active_model.rb

@@ -28,6 +28,7 @@
 require "active_model/version"
 require "active_model/deprecator"
 
+# :include: activemodel/README.rdoc
 module ActiveModel
   extend ActiveSupport::Autoload
 

activerecord/lib/active_record.rb

@@ -34,6 +34,7 @@
 require "active_model/attribute_set"
 require "active_record/errors"
 
+# :include: activerecord/README.rdoc
 module ActiveRecord
   extend ActiveSupport::Autoload
 

activestorage/lib/active_storage.rb

@@ -34,6 +34,8 @@
 
 require "marcel"
 
+# :markup: markdown
+# :include: activestorage/README.md
 module ActiveStorage
   extend ActiveSupport::Autoload
 

activesupport/lib/active_support.rb

@@ -31,6 +31,7 @@
 require "active_support/lazy_load_hooks"
 require "active_support/core_ext/date_and_time/compatibility"
 
+# :include: activesupport/README.rdoc
 module ActiveSupport
   extend ActiveSupport::Autoload
 

railties/lib/rails.rb

@@ -24,6 +24,7 @@
   Encoding.default_internal = Encoding::UTF_8
 end
 
+# :include: railties/README.rdoc
 module Rails
   extend ActiveSupport::Autoload
   extend ActiveSupport::Benchmarkable

railties/lib/rails/api/task.rb

@@ -10,6 +10,7 @@ class Task < RDoc::Task
         "activesupport" => {
           include: %w(
             README.rdoc
+            lib/active_support.rb
             lib/active_support/**/*.rb
           )
         },
@@ -17,6 +18,7 @@ class Task < RDoc::Task
         "activerecord" => {
           include: %w(
             README.rdoc
+            lib/active_record.rb
             lib/active_record/**/*.rb
             lib/arel.rb
           )
@@ -25,6 +27,7 @@ class Task < RDoc::Task
         "activemodel" => {
           include: %w(
             README.rdoc
+            lib/active_model.rb
             lib/active_model/**/*.rb
           )
         },
@@ -41,6 +44,7 @@ class Task < RDoc::Task
         "actionview" => {
           include: %w(
             README.rdoc
+            lib/action_view.rb
             lib/action_view/**/*.rb
           ),
           exclude: "lib/action_view/vendor/*"
@@ -49,6 +53,7 @@ class Task < RDoc::Task
         "actionmailer" => {
           include: %w(
             README.rdoc
+            lib/action_mailer.rb
             lib/action_mailer/**/*.rb
           )
         },
@@ -56,6 +61,7 @@ class Task < RDoc::Task
         "activejob" => {
           include: %w(
             README.md
+            lib/active_job.rb
             lib/active_job/**/*.rb
           )
         },
@@ -63,6 +69,7 @@ class Task < RDoc::Task
         "actioncable" => {
           include: %w(
             README.md
+            lib/action_cable.rb
             lib/action_cable/**/*.rb
           )
         },
@@ -71,6 +78,7 @@ class Task < RDoc::Task
           include: %w(
             README.md
             app/**/active_storage/**/*.rb
+            lib/active_storage.rb
             lib/active_storage/**/*.rb
           )
         },
@@ -79,6 +87,7 @@ class Task < RDoc::Task
           include: %w(
             README.md
             app/**/action_mailbox/**/*.rb
+            lib/action_mailbox.rb
             lib/action_mailbox/**/*.rb
           )
         },
@@ -87,6 +96,7 @@ class Task < RDoc::Task
           include: %w(
             README.md
             app/**/action_text/**/*.rb
+            lib/action_text.rb
             lib/action_text/**/*.rb
           )
         },