Update README and gemspec description

 * Reword the first paragraph for more clarification.

 * Add the compatibility matrix for stable branches and explain the
   maintenance policy.

 * Remove the outdated paragraph for how to use the gem in Ruby 2.3,
   which is no longer supported.

README.md

@@ -2,14 +2,38 @@
 
 [![Actions Status](https://github.com/ruby/openssl/workflows/CI/badge.svg)](https://github.com/ruby/openssl/actions?workflow=CI)
 
+OpenSSL for Ruby provides access to SSL/TLS and general-purpose cryptography
+based on the OpenSSL library.
 
-OpenSSL provides SSL, TLS and general purpose cryptography. It wraps the
-OpenSSL library.
+OpenSSL for Ruby is sometimes referred to as "openssl" (in all lowercase) or
+"Ruby/OpenSSL" for disambiguation.
+
+## Compatibility and maintenance
+
+OpenSSL for Ruby is released as a RubyGems gem. At the same time, it is part of
+the standard library of Ruby. This is called a [default gem].
+
+Stable branches of OpenSSL for Ruby will receive security and bug fixes for the
+[lifecycle of their corresponding Ruby branch][Ruby Maintenance Branches].
+
+|Branch|Maintenance status             |Supported Ruby versions|Supported OpenSSL versions                           |
+|------|-------------------------------|-----------------------|-----------------------------------------------------|
+|3.2   |normal maintenance (Ruby 3.3)  |Ruby >= 2.7            |OpenSSL >= 1.0.2, <= 3.1 (current) or LibreSSL >= 3.1|
+|3.1   |normal maintenance (Ruby 3.2)  |Ruby >= 2.6            |OpenSSL >= 1.0.2, <= 3.1 (current) or LibreSSL >= 3.1|
+|3.0   |normal maintenance (Ruby 3.1)  |Ruby >= 2.6            |OpenSSL >= 1.0.2, <= 3.1 (current) or LibreSSL >= 3.1|
+|2.2   |security maintenance (Ruby 3.0)|Ruby >= 2.3            |OpenSSL >= 1.0.1, <= 1.1.1 or LibreSSL >= 2.9        |
+|2.1   |end-of-life (Ruby 2.5-2.7)     |Ruby >= 2.3            |OpenSSL >= 1.0.1, <= 1.1.1 or LibreSSL >= 2.5        |
+|2.0   |end-of-life (Ruby 2.4)         |Ruby >= 2.3            |OpenSSL >= 0.9.8, <= 1.1.1 or LibreSSL >= 2.3        |
+
+[default gem]: https://docs.ruby-lang.org/en/master/standard_library_rdoc.html
+[Ruby Maintenance Branches]: https://www.ruby-lang.org/en/downloads/branches/
 
 ## Installation
 
-The openssl gem is available at [rubygems.org](https://rubygems.org/gems/openssl).
-You can install with:
+The openssl gem is included with Ruby by default, but newer releases may be
+available at [rubygems.org](https://rubygems.org/gems/openssl).
+
+To upgrade it, you can use RubyGems:
 
 ```
 gem install openssl
@@ -21,7 +45,7 @@ You may need to specify the path where OpenSSL is installed.
 gem install openssl -- --with-openssl-dir=/opt/openssl
 ```
 
-Alternatively, you can install the gem with `bundler`:
+Alternatively, you can install the gem with Bundler:
 
 ```ruby
 # Gemfile
@@ -30,7 +54,7 @@ gem 'openssl'
 gem 'openssl', git: 'https://github.com/ruby/openssl'
 ```
 
-After doing `bundle install`, you should have the gem installed in your bundle.
+After running `bundle install`, you should have the gem installed in your bundle.
 
 ## Usage
 
@@ -40,15 +64,6 @@ Once installed, you can require "openssl" in your application.
 require "openssl"
 ```
 
-**NOTE**: If you are using Ruby 2.3 (and not Bundler), you **must** activate
-the gem version of openssl, otherwise the default gem packaged with the Ruby
-installation will be used:
-
-```ruby
-gem "openssl"
-require "openssl"
-```
-
 ## Documentation
 
 See https://ruby.github.io/openssl/.

openssl.gemspec

@@ -3,8 +3,8 @@ Gem::Specification.new do |spec|
   spec.version       = "3.1.0"
   spec.authors       = ["Martin Bosslet", "SHIBATA Hiroshi", "Zachary Scott", "Kazuki Yamaguchi"]
   spec.email         = ["[email protected]"]
-  spec.summary       = %q{OpenSSL provides SSL, TLS and general purpose cryptography.}
-  spec.description   = %q{It wraps the OpenSSL library.}
+  spec.summary       = %q{SSL/TLS and general-purpose cryptography for Ruby}
+  spec.description   = %q{OpenSSL for Ruby provides access to SSL/TLS and general-purpose cryptography based on the OpenSSL library.}
   spec.homepage      = "https://github.com/ruby/openssl"
   spec.license       = "Ruby"