Add details how setup .env

[otarasovqs]

Hey everyone, I successfully started the app by instruction, but I see the error:

Error: could not detect network (event="noNetwork", code=NETWORK_ERROR, version=providers/5.6.8)

When I looked on the network tab I see a bunch of requests:

https://sepolia.infura.io/v3/undefined

I guess I must set some env variables? But where I get them? Could you clarify this part, please!

[mradkov]

The env vars are explained in this section in the readme.