doc: Add proposed KnownNetworks API

doc/knownnetworks-api.txt

@@ -0,0 +1,42 @@
+KnownNetworks hierarchy
+======================
+
+Service		net.connman.iwd
+Interface	net.connman.iwd.KnownNetworks
+Object path	/
+
+Methods		aa{sv} ListKnownNetworks()
+
+			Returns an array of known networks.  Each array
+			contains a dictionary of string-value pairs.  The
+			type of the value can be determined from the string
+			type.  The following types are supported:
+
+			string Name
+
+				Contains the Name (SSID) of the network
+
+			string Type
+
+				Contains the type of the network.  Possible
+				types are "open", "psk", "eap"
+
+			string LastConnectedTime [optional]
+
+				Contains the last time this network has been
+				connected to.  The time is given as a string
+				in ISO 8601 format.  If the network is known,
+				but has never been successfully connected to,
+				this attribute is omitted.
+
+			string LastSeenTime [optional]
+
+				Contains the last time this network has been
+				seen in scan results.
+
+		void ForgetNetwork(string name, string type)
+
+			Removes the network from the 'known networks' list and
+			removes any associated meta-data.  If the network is
+			currently connected, then it is automatically
+			disconnected.