Add changeset for PR #1037

Add changeset so the change can be released and is shown in the
CHANGELOG.md file upon release.

.changesets/add-instrumentation-for-streaming-rack-responses.md

@@ -0,0 +1,21 @@
+---
+bump: "minor"
+type: "add"
+---
+
+Add instrumentation for all Rack responses, including streaming responses. New `response_body_each.rack`, `response_body_call.rack` and `response_body_to_ary.rack` events will be shown in the event timeline. This will show how long it takes to complete responses, depending on the response implementation.
+
+This Sinatra route with a streaming response will be better instrumented, for example:
+
+```ruby
+get "/stream" do
+  stream do |out|
+    sleep 1
+    out << "1"
+    sleep 1
+    out << "2"
+    sleep 1
+    out << "3"
+  end
+end
+```