Add solutions to common deployment issues in README

[delventhalz]

Specifically these two issues popped up for many students on Linux:

Issues with number of watchers: https://stackoverflow.com/questions/22475849/node-js-error-enospc/32600959#32600959 echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p

Sudo required for every docker command: https://docs.docker.com/install/linux/linux-postinstall/#manage-docker-as-a-non-root-user