Update CONTRIBUTING.md
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ace2634..1f1766e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -46,7 +46,9 @@
Flutter depends on. You can replicate what this script does by running
`pub get` in each directory that contains a `pubspec.yaml` file.
* Add this repository's `bin` directory to your path. That will let you use the
- `flutter` command in this directory more easily.
+ `flutter` command in this directory more easily. (If you have previously
+ activated the `flutter` package using `pub`, you should deactivate it and use
+ the script in `bin` instead: `pub global deactivate flutter`.)
Running the examples
--------------------
