This updates the minimum version for Rust from 1.28 to the current
latest which is 1.33. This is because 1.28 may fail on build due to
It also updates the minimum version of Electrum to the current latest
of 3.3 since version 3.2 is officially unsupported due to a known
phishing vulnerability.
If I don't set a `electrum-rpc-addr` flag, by default electrs only listens for tcp6 connections. In order to accept tcp4, I need to add `--electrum-rpc-addr="127.0.0.1:50001`.
This is not a big deal since setting the flag fixes it, but adding this info to the docs should make it easier for users.
Also, the `config.rs` file should be changed since the help for this option lists `127.0.0.1:50001` as the default, which is not correct (at least on my install).
I also added a sample unit file for systemd.