Feedback on the README usage

Hi,

1) Please update the Discource link in a README file: https://discourse.maas.io/t/setting-up-a-minimal-dev-environment-with-lxd/6318 (404 there).

2) Consider to add `--yes` to `apt` command, otherwise the script stops waiting for the confirmation to install git+make (for no reason, IMHO): https://github.com/canonical/maas-dev-setup/blob/main/setup-dev-env.sh#L85

3) there is an error in the stript:
```
multipass launch -d 50GB -c 8 -m 12GB -n maas 22.04
multipass shell maas
git clone https://github.com/canonical/maas-dev-setup && cd maas-dev-setup
./setup-dev-env.sh --ok
...
Submodule path 'src/maasui/src': checked out 'a0347b47c76615a767748391b379180162962519'
..done
./setup-dev-env.sh: 104: [: !=: unexpected operator
..done
```

The fix is ` if [ -n "${MAAS_LAUNCHPAD_ID}" ]; then`. P.S. shellcheck detects it (and a bit more warnings):
```
sudo snap install shellcheck
shellcheck setup-dev-env.sh
...
In setup-dev-env.sh line 104:
if [ ${MAAS_LAUNCHPAD_ID} != "" ]; then
^------------------^ SC2086 (info): Double quote to prevent globbing and word splitting.
```

4. This is printed to STDERR/STDOUT and scary a bit:
```
cat: /home/ubuntu/.ssh/id_rsa.pub: No such file or directory
```
Should RSA key be generated if missing? Or requested as a precondition?

and actually it has failed:
```
################################################################
SSHing into maas-dev (10.10.0.27) development and setting it up
Warning: Permanently added '10.10.0.27' (ED25519) to the list of known hosts.
ubuntu@10.10.0.27: Permission denied (publickey).
ubuntu@maas:~/maas-dev-setup$ echo $?
255
```

Reinstalling as the script restart is not possible :-D
```
#######################
Setting up LXD networks
Error: The network already exists
```

Thank you for the great automation here! We will use it as a playground hint for Data Platform charms installation on MAAS. Tnx!