Add article with example of interfacing with Stan model

[matt-graham]

Adds an article illustrating how to use rmcmc to sample from posterior distribution defined by a Stan model, using the real-world example of the Hodgkin-Huxley model for action potential generation fitted to voltage clamp experimental data from Hodgkin and Huxley's 1952 paper.

Should resolve #85

Ideally this would also include and example of posterior predictive checks using bayesplot but this will require fixing #89.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4852998) to head (04e6b24).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #90   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          580       580           
=========================================
  Hits           580       580           

☔ 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.