Update instrumentation/action_pack/README.md

Co-authored-by: Kayla Reopelle (she/her) <[email protected]>

instrumentation/action_pack/README.md

@@ -34,7 +34,7 @@ end
 
 Earlier versions of this instrumentation relied on patching custom `dispatch` hooks from Rails's [Action Controller](https://github.com/rails/rails/blob/main/actionpack/lib/action_controller/metal.rb#L224) to extract request information.
 
-This instrumentation now relies on `ActiveSupport::Notifications` and registers a custom Subscriber that listens to relevant events to modify rack span.
+This instrumentation now relies on `ActiveSupport::Notifications` and registers a custom Subscriber that listens to relevant events to modify the Rack span.
 
 See the table below for details of what [Rails Framework Hook Events](https://guides.rubyonrails.org/active_support_instrumentation.html#action-controller) are recorded by this instrumentation: