Revise a cross-ref in docs.md

[star1327p]

Revise a cross-ref in docs.md.

Incorrect:
:class:~arviz_plots.PlotCollection

Correct:
{class}~arviz_plots.PlotCollection

---

📚 Documentation preview 📚: https://arviz-plots--260.org.readthedocs.build/en/260/

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.44%. Comparing base (827cece) to head (c59b3c5).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #260   +/-   ##
=======================================
  Coverage   72.44%   72.44%           
=======================================
  Files          42       42           
  Lines        4921     4921           
=======================================
  Hits         3565     3565           
  Misses       1356     1356           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.