Merge pull request #5274 from plotly/marthacryan-patch-1

Update CONTRIBUTING.md to include jupyter lab local development instr…

Author: marthacryan

CONTRIBUTING.md

@@ -120,6 +120,20 @@ you can install all packages with:
 pip install -e '.[dev]'
 ```
 
+If you're testing local changes in Jupyter Lab or Jupyter Notebook, you'll want to run these commands when you're setting up your development environment:
+```bash
+pip install jupyter
+jupyter labextension develop .
+```
+If you don't run that command, your figure will not render in the Jupyter Lab/ Jupyter Notebook editors. 
+
+If you're changing any of the code under the `js/` directory, you'll also want to run these commands:
+```
+cd js/
+npm ci
+npm run build
+```
+
 These commands also create an *editable install* of plotly.py
 so that you can test your changes iteratively without having to rebuild the plotly.py package explicitly;
 for more information please see