Update frontend/README.md

[MikeyManoguerra]

the script commands are incorrect, and have a typo
to start the application from the front end directory, you need to use the../script/ (singular) directory, and run the scripts sever and setup

here are the updated commands

# start dockerized environment
../script/server
../script/setup

after the yarn commands, Add a clarifying statement that the fully built dockerized front end can be found at localhost:8080, while the development environment can be found at localhost:1234