added hyperlink to refer to 'define environment variable for a container' (#40936)

* added hyperlink to refer to 'define environment variable for a container' to 'deployment'

* hyperlink updated

* 'Deployment' fix and re-wording changes

Author: KhushPatibandha

content/en/docs/concepts/workloads/controllers/deployment.md

@@ -38,6 +38,10 @@ The following are typical use cases for Deployments:
 
 ## Creating a Deployment
 
+Before creating a Deployment define an 
+[environment variable](/docs/tasks/inject-data-application/define-environment-variable-container/#define-an-environment-variable-for-a-container)
+for a container. 
+
 The following is an example of a Deployment. It creates a ReplicaSet to bring up three `nginx` Pods:
 
 {{< codenew file="controllers/nginx-deployment.yaml" >}}