Announce the 2.0.0 pre-release

[jcouball]

• Ensure all commits include DCO sign-off.
• Ensure that your contributions pass unit testing.
• Ensure that your contributions contain documentation if applicable.

Description

Announce the 2.0.0 pre-release in the README.

git 2.0.0 is available as a pre-release version for testing! Please give it a try.

JRuby on Windows is not yet supported by the 2.x release line. Users running JRuby
on Windows should continue to use the 1.x release line.

The changes coming in this major release include:

• Create a policy of supported Ruby versions to support only non-EOL Ruby versions
• Create a policy of supported Git CLI versions (released 2020-12-25)
• Update the required Ruby version to at least 3.0 (released 2020-07-27)
• Update the required Git command line version to at least 2.28
• Update how CLI commands are called to use the process_executer
  gem which is built on top of Kernel.spawn.
  See PR #617 for more details
  on the motivation for this implementation.

The tentative plan is to release 2.0.0 near the end of March 2024 depending on
the feedback received during the pre-release period.

The master branch will be used for 2.x development. If needed, fixes for 1.x
version will be done on the v1 branch.