Update frontend/README.md

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`