In the snek-extenson directory run the following:
npm i && npm start
This will install the necessary packages needed and build the extension (compiled & unpacked extension files are in the "dist" folder).
In Chrome go to chrome://extensions/, Tick the "Developer Mode" option, and click "Load Unpacked". Give it the path to snek-extension/dist.
Any time a source file is saved, the extension will automatically reload.
To run the most recent update, run
git pull # This updates the local code
npm i && npm start