fix: update kusion doc to correct developer role (#526)

Author: kaysonyu

docs/kusion/3-concepts/3-module/3-app-dev-guide.md

@@ -9,7 +9,7 @@ To follow this guide, you will need:
 
 ## Workflow
 
-As a platform engineer, the workflow of developing a Kusion module looks like this:
+As an application developer, the workflow of using a Kusion module looks like this:
 
 1. Browse available modules registered by platform engineers in the workspace
 2. Add modules you need to your Stack