Update CLI tools instructions in README.md

[throwaway96]

The new unified webOS CLI tools (@webos-tools/cli) always prepend ${HOME}/.ssh (or, on Windows, %USERPROFILE%\.ssh) to the private key path. I've updated the installation instructions to reflect that. (Did the instructions ever work? The previous webOS TV CLI tools may have behaved differently.)

It's probably easier to just use ares-novacom --getkey for the Dev Mode instructions, but I didn't feel like setting up Dev Mode to test it. I imagine it would go something like:

ares-setup-device -a webos -i "username=prisoner" -i "passphrase=PASSPHRASE" -i "host=TV_IP" -i "port=9922"
ares-novacom -d webos -k

If someone wants to confirm this works, I can add it.

We could add ares-setup-device -i "default=true" to avoid users having to specify the device on subsequent commands. We may also want to add something about checking that the current profile is tv (ares-config -c) and changing it if not (ares-config -p tv).

I also added -t rsa to ssh-keygen because we refer to id_rsa(.pub). Windows 11 OpenSSH does default to RSA, but on Debian I get Ed25519 by default.

Fixes #180.