NO-ISSUE Add note about Skipper to the operator build docs (#1768)

docs/operator.md

@@ -16,9 +16,13 @@ Build the bundle:
 
 ```
 export BUNDLE_IMAGE=quay.io/${QUAY_NAMESPACE}/assisted-service-operator-bundle:${TAG}
-make operator-bundle-build
+skipper make operator-bundle-build
 ```
 
+**NOTE**
+
+It is possible to run `make` command without using Skipper. In such a scenario all the required dependencies can be installed using the [setup_env.sh script](../hack/setup_env.sh).
+
 ## Deploying the operator
 
 The operator must be deployed to the assisted-installer namespace. Create the namespace.