README.md in config-3.1.1 vs README.md in config-4.0.0

@@ -22,20 +22,22 @@
 ## Compatibility
 
 Current version supports and is [tested](.github/workflows/tests.yml#L19) for the following interpreters and frameworks:
 
 * Interpreters
-  * [Ruby](https://www.ruby-lang.org) `>= 2.4`
+  * [Ruby](https://www.ruby-lang.org) `>= 2.6`
   * [JRuby](https://www.jruby.org) `>= 9.2`
   * [TruffleRuby](https://github.com/oracle/truffleruby) `>= 19.3`
 * Application frameworks
-  * Rails `>= 4.2`, `5` and `6`
+  * Rails `>= 5.2`
   * Padrino
   * Sinatra
 
 For Ruby `2.0` to `2.3` or Rails `3` to `4.1` use version `1.x` of this gem. For older versions of Rails or Ruby use [AppConfig](http://github.com/fredwu/app_config).
 
+For Ruby `2.4` or `2.5` or Rails `4.2`, `5.0`, or `5.1` use version `3.x` of this gem.
+
 ## Installing
 
 ### Installing on Rails
 
 Add `gem 'config'` to your `Gemfile` and run `bundle install` to install it. Then run
@@ -530,9 +532,36 @@
 ## Contributing
 
 You are very warmly welcome to help. Please follow our [contribution guidelines](CONTRIBUTING.md)
 
 Any and all contributions offered in any form, past present or future are understood to be in complete agreement and acceptance with [MIT](LICENSE) license.
+
+### Running specs
+
+Setup
+
+```sh
+bundle install
+bundle exec appraisal install
+```
+
+List defined appraisals:
+
+```sh
+bundle exec appraisal list
+```
+
+Run specs for specific appraisal:
+
+```sh
+bundle exec appraisal rails-6.1 rspec
+```
+
+Run specs for all appraisals:
+
+```sh
+bundle exec appraisal rspec
+```
 
 ## Authors
 
 * [Piotr Kuczynski](http://github.com/pkuczynski)
 * [Fred Wu](http://github.com/fredwu)