Reapply "Add a sample MyST notebook"

This reverts commit d1c7f7d.

Author: agriyakhetarpal

docs/directives/my_notebook.md

@@ -0,0 +1,27 @@
+---
+jupytext:
+  text_representation:
+    extension: .md
+    format_name: myst
+    format_version: 0.13
+    jupytext_version: 1.16.4
+kernelspec:
+  display_name: Python 3 (ipykernel)
+  language: python
+  name: python3
+---
+
+# This is a Jupyter Notebook
+
+```{code-cell} ipython3
+def foo():
+    print(3)
+```
+
+```{code-cell} ipython3
+foo()
+```
+
+```{code-cell} ipython3
+
+```