README.md in rspec-datadog-0.1.2 vs README.md in rspec-datadog-0.2.0

@@ -40,9 +40,13 @@
 end
 ```
 
 Note that all examples in a given run will have a UUID aggregation key added.
 
+*If* you are using rspec 3, the formatter API has changed - you'll need to run
+with `--require rspec/legacy_formatters` and have the `rspec-legacy_formatters`
+gem installed.
+
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at
 https://github.com/lookout/rspec-datadog.  Please see the Contributor License
 Agreement in CONTRIBUTING.