Improve documentation

[x42005e1f]

What do these changes do?

This PR improves the accessibility of the library for new users and shows limitations to consider. It also adds a link to the new culsans library to reduce the chance of irrelevant issues for the janus library.

Are there changes in behavior for the user?

There are no behavior changes for users.

Related issue number

• Closes Use AnyIO (optionally) #506
• Closes #506 anyio integration #507
• Fixes Task was destroyed but it is pending #574
• Fixes Status of project and performance improvements #679

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.34%. Comparing base (d2e195d) to head (53d8179).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #691   +/-   ##
=======================================
  Coverage   94.34%   94.34%           
=======================================
  Files           4        4           
  Lines        1309     1309           
  Branches       78       78           
=======================================
  Hits         1235     1235           
  Misses         66       66           
  Partials        8        8           

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

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests