Merge pull request #6260 from segmentio/joeynmq-patch-2

Update index.md

Author: cmastr

src/connections/destinations/catalog/branch-metrics/index.md

@@ -20,15 +20,20 @@ This destination is maintained by Branch. For any issues with the destination, [
 
 ## Getting Started
 
-
-
   1. From the Segment web app, click **Catalog**.
   2. Search for "Branch Metrics" in the Catalog, select it, and choose which of your sources to connect the destination to.
   3. On Branch side you will need to [sign up for a free Branch account](http://branch.io/signup?bmp=segment){:target="_blank"} and follow the steps on their Dashboard to complete set up.
   4. Copy your `Branch Key` from the Settings page of your [Branch dashboard](https://dashboard.branch.io/#/settings){:target="_blank"}.
   5. Paste the Branch Key in the destination settings and click **Save**.
 
 
+### Identifiers for app events
+
+Identifiers are required for events to be imported to Branch. You must include:
+- `context.device.advertisingId` and `context.os.name` and `context.os.version`, or
+- `context.device.id` and `context.os.name` and `context.os.version`
+
+
 ## Identify
 
 If you're not familiar with the Segment Specs, take a look to understand what the [Identify method](/docs/connections/spec/identify/) does. An example iOS call would look like: