chore: fix broken link in docs (coder#18733)

Fixes the "Helm README" link on
https://coder.com/docs/install/kubernetes so it goes to the right path.

Side note: I don't see any content in
https://coder.com/docs/about/contributing/documentation about to whom
such a PR should be assigned, if any. Edward was suggested and I see
you've worked on other PR's with the `docs` label, so going with that.

Author: rowansmithau

docs/install/kubernetes.md

@@ -117,7 +117,7 @@ coder:
 ```
 
 You can view our
-[Helm README](https://github.com/coder/coder/blob/main/helm#readme) for
+[Helm README](https://github.com/coder/coder/blob/main/helm/coder#readme) for
 details on the values that are available, or you can view the
 [values.yaml](https://github.com/coder/coder/blob/main/helm/coder/values.yaml)
 file directly.