docs: add docs for gluon-web-cellular

docs/index.rst

@@ -73,6 +73,7 @@ Several Freifunk communities in Germany use Gluon as the foundation of their Fre
   package/gluon-radv-filterd
   package/gluon-scheduled-domain-switch
   package/gluon-web-admin
+  package/gluon-web-cellular
   package/gluon-web-network
   package/gluon-web-logging
 

docs/package/gluon-web-cellular.rst

+.. _package-gluon-web-cellular:
+
+gluon-web-cellular
+==================
+
+This package allows the configure WWAN for capable cellular devices.
+
+This works by creating an abstraction layer into Gluon which takes common options (SIM PIN / APN) and translates it to modem-specific settings based on the specific device using. 
+Doing so limits the use-case onto specific models (no LTE sticks possible) but provides a common interface.
+
+The WWAN is assigned the firewall WAN zone and wired WAN can still be used, however without prioritization.
+The traffic path is not configured to prefer one uplink source or the other.
+
+.. image:: gluon-web-cellular.png