Add screencast link to README

Author: itlinde

README.md

@@ -22,6 +22,7 @@ Open the live site and scroll from top to bottom. Scenes 1-3 introduce the core
 - EDA notebook: [`notebooks/exploratory_analysis.ipynb`](notebooks/exploratory_analysis.ipynb)
 - Data aggregation script: [`data/build_aggregates.py`](data/build_aggregates.py)
 - Deployment workflow: [`.github/workflows/deploy.yml`](.github/workflows/deploy.yml)
+- Screencast link: [`https://youtu.be/zW6h9NghxNc`](https://youtu.be/zW6h9NghxNc)
 
 ## Team