https://github.com/ruby/openssl/commit/6b3dd6a372

 * Reword the description in README for more clarity.

 * Add a compatibility matrix of our stable branches and explain the
   maintenance policy.

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

https://github.com/ruby/openssl/commit/7691034fcb

Ruby 2.6 has reached EOL on 2022-03. Requiring Ruby 2.7 allows us to
use C99 syntax.

https://github.com/ruby/openssl/commit/f6ba75e51e

JRuby has its own implementation of the `openssl` library in
jruby-openssl. The simplest way for us to allow users to set
openssl as a gem dependency is to ship a stub gem that just
depends on jruby-openssl. This patch adds that to the gemspec.
Additional work may be required to fit this stub gem into the test
and release process.

See #20 for more details.

https://github.com/ruby/openssl/commit/74ccaa5e18

https://github.com/ruby/openssl/commit/c2f7d775c6

https://github.com/ruby/openssl/commit/fceb978a5d

https://github.com/ruby/openssl/commit/e5bbd015dc

https://github.com/ruby/openssl/commit/bff4080091

Drop support for Ruby 2.3, 2.4, and 2.5.

As of 2021-10, Ruby 2.6 is the oldest version that still receives
security fixes from the Ruby core team, so it doesn't make much sense
to keep code for those ancient versions.

https://github.com/ruby/openssl/commit/3436bd040d