Update image_management.md objectives

Update episode level objectives

episodes/image_management.md

@@ -14,8 +14,9 @@ exercises: 0
 
 After completing this episode, learners will be able to...
 
-- produce an image using repo2docker
-- create/maintain/recommend an image environment to community members
+- explain value of reproducibility provided by images
+- describe how software images are integrated with their hub environment
+- evaluate whether an existing image meets users' software needs
 - manage images available on their hub instance
 
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