Better usage details with some explanations

wireguard/wgportal_peer_install.sh

@@ -5,7 +5,18 @@
 # - verify curl output to prevent overwriting config file with an HTTP answer
 
 _usage() {
-  printf "Usage: %s [options...] <url>\n" "$0"
+  echo "
+  Usage: $0 <command> --url <wgportal_url> [options...]
+
+Commands :
+  -d, --download            only download config file
+  -i, --install             download config file and install the service (UNIMPLEMENTED)
+
+Parameters:
+  -u, --url <url>           Specify your WG Portal base URL
+  -f, --filename <file>     Specify Wireguard filename (default: /etc/wireguard/wg0.conf)
+  "
+  _version
 }
 
 _version() {