🔧 Template: Add .jupytext-sync-ipynb to .gitignore

To write the documentation, it would be ideal to be able to just write in a Jupyter
notebook, so you can just run the cells locally and test the content. However, the
`.ipynb` format is JSON, which is very cumbersome and leads to large and hard to read
diffs.

Jupytext sync is a tool for writing notebooks in `.ipynb` format, and syncing them to a
`.md` file, see:

https://marketplace.visualstudio.com/items?itemName=caenrigen.jupytext-sync

The Markdown format is also used by our supported documentation tools. Here we
add the directory that Jupytext sync creates to the `.gitignore` to avoid committing
the `.ipynb` files it generates.

Author: mbercx

template/.gitignore

@@ -208,3 +208,7 @@ __marimo__/
 
 # MyST documentation build
 docs/_build
+
+# Jupytext sync is a tool for writing notebooks in `.ipynb` format, and syncing them to a `.md` file
+# https://marketplace.visualstudio.com/items?itemName=caenrigen.jupytext-sync
+.jupytext-sync-ipynb