fix(msteams): update installation instructions and image (#14792)

erased one of our test channel names from an image and updated one of
the installation steps

Author: ameliahsu

docs/organization/integrations/notification-incidents/msteams/img/msteams-select-channel.png

@@ -22,7 +22,7 @@ Sentry owner, manager, or admin permissions are required to install this integra
 
    ![Microsoft Teams installation modal](./img/msteams-open-app.png)
 
-3. Pick the channel where you want to set up Sentry. Click "Go".
+3. Select the General channel for the Team you want for the integration. Click "Go".
 
    ![Microsoft Teams installation modal with channel selection](./img/msteams-select-channel.png)