[Config] Add allowed chars for API key

generate_config.sh

@@ -150,6 +150,7 @@ SYSCTL_IPV6_DISABLED=0
 
 # Create or override API key for web uI
 # You _must_ define API_ALLOW_FROM, which is a comma separated list of IPs
+# API_KEY allowed chars: a-z, A-Z, 0-9, -
 #API_KEY=
 #API_ALLOW_FROM=127.0.0.1,1.2.3.4