Document EncryptedConfiguration access methods [ci-skip]

activesupport/lib/active_support/encrypted_configuration.rb

@@ -7,6 +7,28 @@ require "active_support/core_ext/object/inclusion"
 require "active_support/core_ext/module/delegation"
 
 module ActiveSupport
+  # Provides convenience methods on top of EncryptedFile to access values stored
+  # as encrypted YAML.
+  #
+  # Values can be accessed via +Hash+ methods, such as +fetch+ and +dig+, or via
+  # dynamic accessor methods, similar to OrderedOptions.
+  #
+  #   my_config = ActiveSupport::EncryptedConfiguration.new(...)
+  #   my_config.read # => "some_secret: 123\nsome_namespace:\n  another_secret: 456"
+  #
+  #   my_config[:some_secret]
+  #   # => 123
+  #   my_config.some_secret
+  #   # => 123
+  #   my_config.dig(:some_namespace, :another_secret)
+  #   # => 456
+  #   my_config.some_namespace.another_secret
+  #   # => 456
+  #   my_config.fetch(:foo)
+  #   # => KeyError
+  #   my_config.foo!
+  #   # => KeyError
+  #
   class EncryptedConfiguration < EncryptedFile
     class InvalidContentError < RuntimeError
       def initialize(content_path)