Ledger Fix script for Arch Linux and Linux users

Thanks for PR! A couple of points:

This is not a Bob or Handshake problem, it's related to setting up ledger software to be used by any wallet (kelpr, metamask, etc.) and even Ledger's official manager app.
Having said that, it can be useful to mention it somewhere, like in the readme / install instructions.
This applies to Linux distros in general, not just Arch
It's not only for development, any kind ledger connection won't work even for regular users (Bob, other wallets) who download the software and run.
The npm install hsd-ledger is no longer required, it's already included.

Instead, how about we add a note at the end of How to Install Bob Wallet in the README like:

For Linux users, if your Ledger device isn't showing up in the Ledger Live app and Bob cannot find it, some [udev rules might need to be set up](https://support.ledger.com/hc/en-us/articles/115005165269-Fix-USB-connection-issues-with-Ledger-Live?support=true) with:

```sh
wget -q -O - https://raw.githubusercontent.com/LedgerHQ/udev-rules/master/add_udev_rules.sh | sudo bash
```

kyokan / bob-wallet

Ledger Fix script for Arch Linux and Linux users #591