Add deprecation message

Author: JonRowe

README.md

@@ -1,70 +1,3 @@
-# RSpec::ActiveModel::Mocks [![Build Status](https://secure.travis-ci.org/rspec/rspec-activemodel-mocks.svg?branch=master)](http://travis-ci.org/rspec/rspec-activemodel-mocks)
+# RSpec::ActiveModel::Mocks
 
-RSpec::ActiveModel::Mocks provides tools for testing `ActiveModel` classes.
-
-    mock_model(Person, name: "Fred")
-
-## Install
-
-Add this line to your application's gemfile:
-
-    gem 'rspec-activemodel-mocks'
-
-And then execute:
-
-    $ bundle
-
-If you are using [rspec-rails](https://github.com/rspec/rspec-rails) and have
-followed the installation instructions there, you're all set to use `stub_model`
-and `mock_model`.
-
-To use `stub_model` and `mock_model` without rspec-rails, require the
-following file:
-
-    require 'rspec/active_model/mocks'
-
-## Usage
-
-### Mock
-
-Creates a test double representing `string_or_model_class` with common
-ActiveModel methods stubbed out. Additional methods may be easily stubbed
-(via `add_stubs`) if `stubs` is passed. This is most useful for impersonating
-models that don't exist yet.
-
-ActiveModel methods, plus `new_record?`, are stubbed out implicitly.
-`new_record?` returns the inverse of `persisted?`, and is present only for
-compatibility with extension frameworks that have yet to update themselves to
-the ActiveModel API (which declares `persisted?`, not `new_record?`).
-
-`string_or_model_class` can be any of:
-
-  * A String representing a Class that does not exist
-  * A String representing a Class that extends `ActiveModel::Naming`
-  * A Class that extends `ActiveModel::Naming`
-
-### Stub
-
-Creates an instance of `Model` with `to_param` stubbed using a generated value
-that is unique to each object. If `Model` is an `ActiveRecord` model, it is
-prohibited from accessing the database.
-
-For each key in `stubs`, if the model has a matching attribute (determined by
-`respond_to?`) it is simply assigned the submitted values.  If the model does
-not have a matching attribute, the key/value pair is assigned as a stub return
-value using RSpec's mocking/stubbing framework.
-
-`persisted?` is overridden to return the result of `!id.nil?` This means that
-by default `persisted?` will return true. If you want the object to behave as a
-new record, sending it `as_new_record` will set the id to nil. You can also
-explicitly set `:id => nil`, in which case `persisted?` will return false, but
-using `as_new_record` makes the example a bit more descriptive.
-
-While you can use `stub_model` in any example (model, view, controller,
-helper), it is especially useful in view examples, which are inherently more
-state-based than interaction-based.
-
-    stub_model(Person)
-    stub_model(Person).as_new_record
-    stub_model(Person, :to_param => 37)
-    stub_model(Person) {|person| person.first_name = "David"}
+This branch is deprecated, please use `main`.

lib/rspec/active_model/mocks.rb

@@ -1,3 +1,5 @@
+warn "This branch is deprecated. Please use `main`."
+:Gwq
 require 'rspec/core'
 
 RSpec::configure do |c|