Add watch_events Makefile target

[aduth]

🛠 Summary of changes

Adds and documents a new Makefile helper command used to watch live event logging.

I've had a version of this command in my local .zshrc file, and recently I've found myself sharing it with others who are troubleshooting event logging in their local environment.

📜 Testing Plan

1. Run make run and make watch_events in separate terminal processes.
2. Go to http://localhost:3000
3. Navigate the application
4. Observe as events are pretty-printed as you navigate the application, using jq

👀 Screenshots

Appearance may vary by terminal customization settings

[jmdembe]

👍🏾