Added missing .env configuration option.

.env.template

@@ -83,6 +83,10 @@
 ## Useful to hide other servers in the local network. Check the WIKI for more details
 # ICON_BLACKLIST_REGEX=192\.168\.1\.[0-9].*^
 
+## Any IP which is not defined as a global IP will be blacklisted.
+## Usefull to secure your internal environment: See https://en.wikipedia.org/wiki/Reserved_IP_addresses for a list of IPs which it will block
+# ICON_BLACKLIST_NON_GLOBAL_IPS=true
+
 ## Disable 2FA remember
 ## Enabling this would force the users to use a second factor to login every time.
 ## Note that the checkbox would still be present, but ignored.