Link to the Image Update guide

When fluxcd/website#702 merges, this patch will
have been incorporated into the Image Update Guide. Add a link to the
more directly relevant Image Update Guide here instead, since it has the
example, and it doesn't belong in the API docs nor need to be repeated
here, per the discussion from the earlier PR number fluxcd#193.

Signed-off-by: Kingdon Barrett <kingdon@weave.works>

docs/spec/v1beta1/imagerepositories.md

@@ -82,23 +82,12 @@ the controller retrieving credentials automatically.
 The `image-reflector-controller` must be run with the flag `--aws-autologin-for-ecr` set for this to work.
 
 This flag can be added by including a patch in the `kustomization.yaml` overlay file in your `flux-system`,
-similar to the process described in [customize Flux manifests][]:
+as described in [Using Native AWS ECR Auto-Login][]. If there is no need for a security boundary on your
+cluster around container registries and you are not using Flux with so-called "soft multi-tenancy", then
+you will likely prefer to use the Auto-Login feature for the convenience and improved ease of use.
 
-```
-patches:
-  - target:
-      version: v1
-      group: apps
-      kind: Deployment
-      name: image-reflector-controller
-      namespace: flux-system
-    patch: |-
-      - op: add
-        path: /spec/template/spec/containers/0/args/-
-        value: --aws-autologin-for-ecr
-```
-
-Alternatively, the advice under [Other platforms][other platforms] below will also work for ECR.
+Alternatively, the advice to use a cron job to refresh a secret token under [Other platforms][other platforms]
+below will also work with ECR for any environment that requires security boundaries and soft multi-tenancy.
 
 #### Other platforms
 
@@ -280,7 +269,7 @@ and reference it under `secretRef`.
 [sops-guide]: https://toolkit.fluxcd.io/guides/mozilla-sops/
 [EKS]: https://docs.aws.amazon.com/eks/latest/userguide/what-is-eks.html
 [ECR]: https://docs.aws.amazon.com/AmazonECR/latest/userguide/what-is-ecr.html
-[customize Flux manifests]: https://fluxcd.io/docs/installation/#customize-flux-manifests
+[Using Native AWS ECR Auto-Login]: https://fluxcd.io/docs/guides/image-update/#using-native-aws-ecr-auto-login
 [other platforms]: https://fluxcd.io/docs/components/image/imagerepositories/#other-platforms
 [Flux v0.19.0]: https://github.com/fluxcd/flux2/releases/tag/v0.19.0
 [image-reflector-controller v0.13.0]: https://github.com/fluxcd/image-reflector-controller/blob/main/CHANGELOG.md#0130