Update README.rst

[lheagy]

update installation instructions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.93%. Comparing base (27a37a5) to head (b8b3f19).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #82   +/-   ##
=======================================
  Coverage   85.93%   85.93%           
=======================================
  Files          31       31           
  Lines        3149     3149           
=======================================
  Hits         2706     2706           
  Misses        443      443           

☔ 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.

[jcapriot]

We can also add instructions about installing with the optional compiled extensions modules.

The relevant command would be:

pip install . --config-settings=setup-args="-Dwith_extensions=true"

[jcapriot]

We can also add instructions about installing with the optional compiled extensions modules.

The relevant command would be:

pip install . --config-settings=setup-args="-Dwith_extensions=true"

And maybe mention that the wheel files on pypi and the version installable through conda-forge come with these extensions pre-built.

[jcapriot]

Just realizing I left this as pending...