Update README.md

[ahcorde]

🦟 Documentation fix

Fixes gazebosim/gazebo_test_cases#45

Summary

Fix link and added missing description folders

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 #534 (2936388) into gz-common5 (e18906b) will not change coverage.
The diff coverage is n/a.

❗ Current head 2936388 differs from pull request most recent head 75af09a. Consider uploading reports for the commit 75af09a to get more accurate results

@@             Coverage Diff             @@
##           gz-common5     #534   +/-   ##
===========================================
  Coverage       83.65%   83.65%           
===========================================
  Files              90       90           
  Lines           10249    10249           
===========================================
  Hits             8574     8574           
  Misses           1675     1675