Clarify isConnected usage to clearly demonstrate bool return case

Related to discussion on #1015

README.md

@@ -838,9 +838,13 @@ Function `stopNotification` stops a previously registered notification callback.
 Reports the connection status.
 
 ```javascript
+// Callbacks
 ble.isConnected(device_id, success, failure);
 // Or using await with promises
-await ble.withPromises.isConnected(device_id);
+const isConnected = await ble.withPromises
+    .isConnected(device_id)
+    .then(() => true)
+    .catch(() => false);
 ```
 
 ### Description
@@ -858,6 +862,7 @@ NOTE that for many apps isConnected is unncessary. The app can track the connect
 ### Quick Example
 
 ```javascript
+// Callbacks
 ble.isConnected(
     'FFCA0B09-CB1D-4DC0-A1EF-31AFD3EDFB53',
     function () {
@@ -867,6 +872,14 @@ ble.isConnected(
         console.log('Peripheral is *not* connected');
     }
 );
+
+// Promises
+try {
+    await ble.withPromises.isConnected(device_id);
+    console.log('Peripheral is connected');
+} catch (e) {
+    console.log('Peripheral is *not* connected');
+}
 ```
 
 ## isEnabled

types.d.ts

@@ -160,7 +160,8 @@ declare namespace BLECentralPlugin {
         ): Promise<void>;
         stopNotification(device_id: string, service_uuid: string, characteristic_uuid: string): Promise<void>;
 
-        /* Returns a rejected promise if the device is not connected */
+        /* Returns a resolved promise if the device is connected,
+            otherwise returns rejected promise if the device is not connected */
         isConnected(device_id: string): Promise<void>;
 
         /* Returns a rejected promise if bluetooth is not connected */