describe the `go get` step before `cue get go` in the tutorial

see #95.  Still needs to be done for the docs in cuelang.org website.

Closes #180
https://github.com/cuelang/cue/pull/180

GitOrigin-RevId: a3cb34161e7aa24bafb8a5297c99a0c575280936
Change-Id: Ib57b868660239807a6944a133e79f2e92eaab53a
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/4080
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/tutorial/kubernetes/README.md b/doc/tutorial/kubernetes/README.md
index 4ee15fb..70f72d5 100644
--- a/doc/tutorial/kubernetes/README.md
+++ b/doc/tutorial/kubernetes/README.md
@@ -1050,6 +1050,14 @@
 
 ### Extract CUE templates directly from Kubernetes Go source
 
+In order for `cue get go` to generate the CUE templates from Go sources, you first need to have the sources locally:
+
+```
+$ go get k8s.io/api/apps/v1
+$ go get k8s.io/api/extensions/v1beta1
+$ go get k8s.io/api/apps/v1beta1
+```
+
 ```
 $ cue get go k8s.io/api/core/v1
 $ cue get go k8s.io/api/extensions/v1beta1