Parsing .env boolean values

[jiachen247]

Currently, in .env REACT_APP_USE_BACKEND= is left empty to set to false and setting any value here results in using the backend.

This is really counter intuitive, we should pattern match the value here to 1/true/ or 0/false to use or not use the backend respectively.

keep in mind that dotenv parses all valuse as strings
motdotla/dotenv#51

And then update the readme and template .env

[LeowWB]

will look into this

[jiachen247]

closed with #430