add documentation to build docs using a venv

[maurerle]

Description

This improves docs for venv users to build the docs locally

Checklist

• Documentation updated (docstrings, READMEs, user guides, inline comments, doc folder updates etc.)
• Consent to release this PR's code under the GNU Affero General Public License v3.0

Additional Notes (optional)

Verified using conda and venv with and without local installed pandoc

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.61%. Comparing base (095f342) to head (5cc4b71).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #698   +/-   ##
=======================================
  Coverage   45.61%   45.61%           
=======================================
  Files          54       54           
  Lines        8030     8030           
=======================================
  Hits         3663     3663           
  Misses       4367     4367           

Flag	Coverage Δ
pytest	45.61% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ 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.