Remove Windows 7 and align with other README.md's

[Bi0T1N]

🦟 Bug fix

Summary

• remove Windows 7
• align description style with other README files
• update version of links
• fix link for documentation

related to gazebosim/gazebo_test_cases#133

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #122 (5590c46) into gz-plugin2 (f51c800) will not change coverage.
The diff coverage is n/a.

❗ Current head 5590c46 differs from pull request most recent head 62e1f74. Consider uploading reports for the commit 62e1f74 to get more accurate results

@@             Coverage Diff             @@
##           gz-plugin2     #122   +/-   ##
===========================================
  Coverage       98.26%   98.26%           
===========================================
  Files              23       23           
  Lines             748      748           
===========================================
  Hits              735      735           
  Misses             13       13