install.sh: finish with next steps, like bamboo's

The installer no longer opens an editor or starts the service on a fresh
install. It writes the files, then prints: sudoedit the env file, systemctl
start, journalctl -f. --start starts (or restarts) the service straight away,
and an already running service is restarted on upgrade.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -66,13 +66,20 @@ curl -fsSL https://git.veillax.com/Veillax/megalodon/raw/branch/main/deploy/inst
 ```
 
 This downloads the latest release (checking its SHA-256), installs `/usr/local/bin/megalodon`,
-creates a `megalodon` user, `/etc/megalodon/` (settings) and `/var/lib/megalodon/` (data), opens
-`/etc/megalodon/megalodon.env` in your editor, then starts the service and prints the first-run
-admin password. Run it again to upgrade; your settings are kept.
+creates a `megalodon` user, `/etc/megalodon/` (settings) and `/var/lib/megalodon/` (data), and writes
+the systemd service and `/etc/megalodon/megalodon.env`. It then tells you what to do next:
 
-Options: `--version v0.1.0`, `--listen 0.0.0.0:8480`, `--source` (build from the repository with Go
-instead), `--no-edit`, `--no-start`, and `--uninstall` (add `--purge` to delete settings and data).
-Download the script and read it first if you prefer: it is [`deploy/install.sh`](deploy/install.sh).
+```sh
+sudoedit /etc/megalodon/megalodon.env
+sudo systemctl start megalodon
+journalctl -u megalodon -f        # a first install prints the admin password here, once
+```
+
+Run it again to upgrade; your settings are kept and a running service is restarted.
+
+Options: `--start` (start the service straight away), `--version v0.1.0`, `--listen 0.0.0.0:8480`,
+`--source` (build from the repository with Go instead), and `--uninstall` (add `--purge` to delete
+settings and data). Download the script and read it first if you prefer: it is [`deploy/install.sh`](deploy/install.sh).
 
 ## Running it by hand