Add Query-Requirement for Android 11 and later (#335)

We use some features from Java 8, so your project needs also to be compiled with (at least) this version.

For Android 11 and later you may need to add queries to your app's manifest file. It will not find the nextcloud-app otherwise.

```

   <queries>

      <package android:name="com.nextcloud.client" />

      <package android:name="com.nextcloud.android.beta" />

   </queries>

```

### 2) To choose an account, include the following code in your login dialog:

From an Activity