📝 Improve documentation

Author: pboling

README.md

@@ -21,6 +21,15 @@ This gem is compatible with, as of Feb 2021, version 3:
 
 * Latest released version of omniauth, v2.0.2
 * Ruby 2.4, 2.5, 2.6, 2.7, 3.0, ruby-head
+* At least 5 different database ORM adapters, which connect to 15 different database clients!
+
+| Databases | Adapter Libraries |
+|--------- | -------- |
+| MySQL, PostgreSQL, SQLite3 | [ActiveRecord](https://guides.rubyonrails.org/active_record_basics.html) |
+| CouchDB | [CouchPotato](https://github.com/langalex/couch_potato) |
+| MongoDB | [Mongoid](https://github.com/mongodb/mongoid) |
+| RethinkDB | [NoBrainer](http://nobrainer.io/) |
+| ADO, Amalgalite, IBM_DB, JDBC, MySQL, Mysql2, ODBC, Oracle, PostgreSQL, SQLAnywhere, SQLite3, and TinyTDS | [Sequel](http://sequel.jeremyevans.net) |
 
 ## Installation
 

lib/omniauth/identity/models/active_record.rb

@@ -5,6 +5,9 @@
 module OmniAuth
   module Identity
     module Models
+      # ActiveRecord is an ORM for MySQL, PostgreSQL, and SQLite3:
+      #   https://guides.rubyonrails.org/active_record_basics.html
+      # NOTE: ActiveRecord is based on ActiveModel.
       class ActiveRecord < ::ActiveRecord::Base
         include ::OmniAuth::Identity::Model
         include ::OmniAuth::Identity::SecurePassword

lib/omniauth/identity/models/couch_potato.rb

@@ -5,9 +5,11 @@
 module OmniAuth
   module Identity
     module Models
-      # can not be named CouchPotato since there is a class with that name
+      # CouchPotato is an ORM adapter for CouchDB:
+      #   https://github.com/langalex/couch_potato
       # NOTE: CouchPotato is based on ActiveModel.
       # NOTE: CouchPotato::Persistence must be included before OmniAuth::Identity::Models::CouchPotatoModule
+      # NOTE: Includes "Module" in the name for invalid legacy reasons. Rename only with a major version bump.
       module CouchPotatoModule
         def self.included(base)
           base.class_eval do

lib/omniauth/identity/models/mongoid.rb

@@ -5,6 +5,8 @@
 module OmniAuth
   module Identity
     module Models
+      # Mongoid is an ORM adapter for MongoDB:
+      #   https://github.com/mongodb/mongoid
       # NOTE: Mongoid is based on ActiveModel.
       module Mongoid
         def self.included(base)

lib/omniauth/identity/models/nobrainer.rb

@@ -5,7 +5,8 @@
 module OmniAuth
   module Identity
     module Models
-      # http://nobrainer.io/ an ORM for RethinkDB
+      # NoBrainer is an ORM adapter for RethinkDB:
+      #   http://nobrainer.io/
       # NOTE: NoBrainer is based on ActiveModel.
       module NoBrainer
         def self.included(base)

lib/omniauth/identity/models/sequel.rb

@@ -5,7 +5,9 @@
 module OmniAuth
   module Identity
     module Models
-      # http://sequel.jeremyevans.net/ an SQL ORM
+      # Sequel is an ORM adapter for the following databases:
+      #   ADO, Amalgalite, IBM_DB, JDBC, MySQL, Mysql2, ODBC, Oracle, PostgreSQL, SQLAnywhere, SQLite3, and TinyTDS
+      # The homepage is: http://sequel.jeremyevans.net/
       # NOTE: Sequel is *not* based on ActiveModel, but supports the API we need, except for `persisted?`:
       # * create
       # * save