chore(core): Display status on readme

[Tranquility2]

Make the Readme display some more details regarding the project:

• using ruff (just a nice reference)
• pypi version (good visibility)
• license (good visibility)
• supported python versions (good visibility)
• code coverage reporting (main driver for this PR)

Relates to #544 - export code coverage (e.g. to codecov)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (main@54c88cf). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #589   +/-   ##
=======================================
  Coverage        ?   74.95%           
=======================================
  Files           ?       10           
  Lines           ?      547           
  Branches        ?       78           
=======================================
  Hits            ?      410           
  Misses          ?      110           
  Partials        ?       27           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Tranquility2]

https://github.com/testcontainers/testcontainers-python/actions/runs/9276601581/job/25524084272

error - 2024-05-28 21:31:54,280 -- Upload failed: {"detail":"Tokenless has reached GitHub rate limit. 
Please upload using a token: https://docs.codecov.com/docs/adding-the-codecov-token. 
Expected available in 221 seconds."}

Looks like CODECOV_TOKEN is needed in secrets