Update Telemetry matcher in Readme (#25)

Co-authored-by: Zach Daniel <[email protected]>

README.md

@@ -50,7 +50,9 @@ config :my_app, MyApp.Repo,
 
 ```elixir
 # in application.ex
-:ok = :telemetry.attach("spandex-query-tracer-repo_name", [:my_app, :repo_name, :query], &SpandexEcto.TelemetryAdapter.handle_event/4, nil)
+# If your repo is called `MyApp.Repo`, use `[:my_app, :repo, :query]`
+# If your repo is called `Foo.Bar.Baz`, use `[:foo, :bar, :baz, :query]`
+:ok = :telemetry.attach("spandex-query-tracer-repo_name", [:my_app, :repo, :query], &SpandexEcto.TelemetryAdapter.handle_event/4, nil)
 ```
 
 > NOTE: **If you are upgrading from Ecto 2**, make sure to **remove** the `loggers`