added warning about referencing dependencies in pre-install and pre-update

doc/articles/scripts.md

@@ -41,6 +41,8 @@ Composer fires the following named events during its execution process:
 - **post-create-project-cmd**: occurs after the `create-project` command is
   executed.
 
+**NOTE: Composer makes no assumptions about the state of your dependencies prior to `install` or `update`. Therefore, you should not specify scripts that require Composer-managed dependencies in the `pre-update` or `pre-install` event hooks. If you need to execute scripts prior to `install` or `update` please make sure they are self-contained within your root package.
+
 ## Defining scripts
 
 The root JSON object in `composer.json` should have a property called