[Docs] RPC port numbers

[conanoc]

It seems there is no docs for port numbers of RPCs such as web3, grpc, etc. Also, I'm not sure if they are configurable or not.

[compleatang]

We'd love a quick PR on this if you were able.

The ports are, indeed, configurable, via the config file you use. We dump defaults into the default config file provided when burrow config is ran.

If you'd like to see the defaults quickly in your terminal you can run burrow spec -f1 | burrow configure -s-

[deepakchethan]

I would like to work on this if it nobody started working on this.

[gregdhill]

Please go ahead @deepakchethan!