Improve README

* Make Ecto 3 config the default
* Describe how to override config in :telemetry.attach/4

README.md

@@ -6,7 +6,7 @@
 [![Hex pm](http://img.shields.io/hexpm/v/spandex_ecto.svg?style=flat)](https://hex.pm/packages/spandex_ecto)
 [![SourceLevel](https://sourcelevel.io/github/spandex-project/spandex_ecto.svg)](https://sourcelevel.io/github/spandex-project/spandex_ecto)
 
-Tools for integrating Ecto with Spandex
+Tools for integrating Ecto with Spandex.
 
 ## Limitations
 
@@ -30,35 +30,46 @@ end
 
 ## Configuration
 
+Configure `SpandexEcto` globally in your application config:
+
 ```elixir
+# config/config.exs
+
 config :spandex_ecto, SpandexEcto.EctoLogger,
   service: :ecto, # Optional
   tracer: MyApp.Tracer, # Required
 ```
 
-### For Ecto 2
+Then attach it to your repository's telemetry events:
 
 ```elixir
-# Be aware that this is a *compile* time configuration. As such, if you change this you
-# may need to `mix compile --force` and/or `mix deps.compile --force ecto`
-config :my_app, MyApp.Repo,
-  loggers: [{Ecto.LogEntry, :log, [:info]}, {SpandexEcto.EctoLogger, :trace, ["database_name"]}]
-
+# lib/my_app/application.ex
+
+:telemetry.attach(
+  "spandex-query-tracer",
+  # this should match your repo's telemetry prefix
+  [:my_app, :repo, :query],
+  &SpandexEcto.TelemetryAdapter.handle_event/4,
+  # this config will override the global config
+  tracer: MyApp.OtherTracer
+)
 ```
 
-### For Ecto 3
+> NOTE: **If you are upgrading from Ecto 2**, make sure to **remove** the `loggers`
+> entry from your configuration after adding `:telemetry.attach/4`.
 
-```elixir
-# in application.ex
-:telemetry.attach("spandex-query-tracer", [:my_app, :repo_name, :query], &SpandexEcto.TelemetryAdapter.handle_event/4, nil)
-```
+### Ecto 2
 
-> NOTE: **If you are upgrading from Ecto 2**, make sure to **remove** the `loggers`
-> entry from your configuration after adding the `:telemetry.attach`.
+To integrate `SpandexEcto` with pre-`:telemetry` versions of Ecto you need to add `SpandexEcto.EctoLogger` as a logger to your repository.
 
-If your repo is not named like `MyApp.Repo`, you'll need to set `:telemetry_prefix` in your repo config:
+Be aware that this is a *compile* time configuration. As such, if you change this you may need to `mix compile --force` and/or `mix deps.compile --force ecto`.
 
 ```elixir
-config :my_app, MyApp.Something.RepoName,
-  telemetry_prefix: [:my_app, :repo_name]
+# config/config.exs
+
+config :my_app, MyApp.Repo,
+  loggers: [
+    {Ecto.LogEntry, :log, [:info]},
+    {SpandexEcto.EctoLogger, :trace, ["database_name"]}
+  ]
 ```