Update config-page info-text about MQTT topic structure (explain VALUE_NAME)

sd-card/html/edit_config_param.html

@@ -611,8 +611,12 @@ textarea {
 				<input type="text" id="MQTT_MainTopic_value1">
 			</td>
 			<td style="font-size: 80%;">
-				MQTT main topic, under which the counters are published. The single value will be published with the following key: MAINTOPIC/VALUE_NAME/PARAMETER <br>
-				where parameters are: value, rate, timestamp, error<br>
+				MQTT main topic, under which the counters are published. <br>
+				The single value will be published with the following key: MAINTOPIC/VALUE_NAME/PARAMETER where
+				<ul>
+					<li> VALUE_NAME is the name of the value (a meter might have more than one value) as defined during analog and digital ROI configuration (defaults to "main")</li>
+					<li> and PARAMETERS are: value, rate, timestamp, error</li>
+				</ul>
 				The general connection status can be found in MAINTOPIC/CONNECTION
 			</td>
 		</tr>