docs: add a reference to the Xeus kernel template (#152)

* List available kernels, add link to Xeus kernel

* Tenplate, not theme

Co-authored-by: Jeremy Tuloup <jeremy.tuloup@gmail.com>

---------

Co-authored-by: Jeremy Tuloup <jeremy.tuloup@gmail.com>

README.md

@@ -27,3 +27,11 @@ For more info, keep an eye on the JupyterLite documentation:
 
 - How-to Guides: https://jupyterlite.readthedocs.io/en/latest/howto/index.html
 - Reference: https://jupyterlite.readthedocs.io/en/latest/reference/index.html
+
+This template provides the Pyodide kernel (`jupyterlite-pyodide-kernel`), the JavaScript kernel (`jupyterlite-javascript-kernel`), and the p5 kernel (`jupyterlite-p5-kernel`), along with other
+optional utilities and extensions to make the JupyterLite experience more enjoyable. See the
+[`requirements.txt` file](requirements.txt) for a list of all the dependencies provided.
+
+For a template based on the Xeus kernel, see the [`jupyterlite/xeus-python-demo` repository](https://github.com/jupyterlite/xeus-python-demo)
+
+