Fix README example link

[Mirochill]

Summary

• replace the removed notebook/nbviewer README link with the published example usage page
• keep the README pointing at the current documentation for PropkaTraj examples

Closes #79

Validation

• git diff --check
• Confirmed https://becksteinlab.github.io/propkatraj/usage/examples.html returns HTTP 200
• Not run locally (README-only change)

Remote status

• Read the Docs build 32841694 currently fails while evaluating docs/sphinx/conf.py, because propka==3.1.0 imports pkg_resources under the Python 3.14 docs environment. This happens before the README link change is exercised.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.30%. Comparing base (23ca6de) to head (f6524f2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #82   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files           2        2           
  Lines          59       59           
=======================================
  Hits           58       58           
  Misses          1        1           

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[orbeckst]

Thank you for the fix!