Add help text for rundev.sh

rundev.sh

@@ -1,12 +1,19 @@
 #!/bin/bash
 set -euo pipefail
 
+if [[ "${1:-}" == --help ]] || [[ "${1:-}" == -h ]]; then
+	echo "Feathermost rundev.sh: Run two things:" >&2
+	echo "  - a HTTP server to serve the web application" >&2
+	echo "  - a proxy server for a Mattermost instance to avoid CORS problems" >&2
+	exit
+fi
+
 cd "$(dirname "$0")"
 
 if [[ ! -f config ]]; then
 	read -p 'Server URL (e.g. `https://mattermost.example.com`): ' MATTERMOST_REMOTE
 	echo "MATTERMOST_REMOTE='${MATTERMOST_REMOTE//\//}'" > config
-	echo 'You can change this later by editing the file `config`.'
+	echo 'You can change this later by editing the file `config`.' >&2
 fi
 source "config"