Add note about environment variable overriding

Closes: #3195

docs/tasks/inject-data-application/define-environment-variable-container.md

@@ -64,6 +64,10 @@ Pod:
 
 1. To exit the shell, enter `exit`.
 
+**Note:** The environment variables set using the `env` or `envFrom` field
+would override the ones specified in the container image.
+{: .note}
+
 {% endcapture %}
 
 {% capture whatsnext %}