Add documentation for plausible analytics

docs/user_guide/analytics.rst

@@ -12,3 +12,20 @@ Google Analytics' javascript is included in the html pages.
    html_theme_options = {
        "google_analytics_id": "G-XXXXXXXXXX",
    }
+
+Plausible Analytics
+===================
+
+Alternatively https://plausible.io can be used to gather simple
+and privacy-friendly analytics for the site. The dashboard can be accessed
+at ``url/domain``.
+The Scientific-Python community can offer a self-hosted server.
+
+Plausible' javascript is included in the html pages.
+
+.. code:: python
+
+   html_theme_options = {
+       "plausible_analytics_domain": "my-domain",
+       "plausible_analytics_url": "https://.../script.js",
+   }