docs: add private WLAN

docs/features/private-wlan.rst

+Private WLAN
+============
+
+It is possible to set up a private WLAN that bridges the WAN port and is seperated from the mesh network.
+Please note that you should not enable ``mesh_on_wan`` simultaneously.
+
+The private WLAN can be enabled through the config mode if the package ``gluon-luci-privatewifi`` is installed.
+You may also enable a private WLAN using the command line:
+
+  ::
+  uci set wireless.wan_radio0=wifi-iface
+  uci set wireless.wan_radio0.device=radio0
+  uci set wireless.wan_radio0.network=wan
+  uci set wireless.wan_radio0.mode=ap
+  uci set wireless.wan_radio0.encryption=psk2
+  uci set wireless.wan_radio0.ssid="$SSID"
+  uci set wireless.wan_radio0.key="$KEY"
+  uci set wireless.wan_radio0.disabled=0
+  uci commit
+  wifi
+
+Please replace ``$SSID`` by the name of the WLAN and ``$KEY`` by your passphrase (8-63 characters).
+If you have two radios (e.g. 2.4 and 5 GHz) you need to do this for radio0 and radio1.
+
+It may also be disabled by running:
+
+  ::
+  uci set wireless.wan_radio0.disabled=1
+  uci commit
+  wifi

docs/index.rst

@@ -24,6 +24,7 @@ Features
 
    features/configmode
    features/autoupdater
+   features/private-wlan
    features/mesh-on-wan
    features/announce