Updated link to "operator-manifests YAML" as /docs/user (#152)

* Prior blob link to cass-operator-manifests.yaml was a 404

Updated link on line 81 to page that allows user to decide which version YAML they want. Related to https://github.com/datastax/cass-operator/issues/134.

* 2nd update of line 81, change link to /docs/user

docs/user/README.md

@@ -78,7 +78,7 @@ following:
 Generally, `cluster-admin` privileges are required to register a
 `CustomResourceDefinition` (CRD). All privileges needed by the operator are
 present within the
-[operator-manifests YAML](cass-operator-manifests.yaml).
+[operator-manifests YAML](/docs/user).
 _Note the operator does not require `cluster-admin` privileges, only the user
 defining the CRD requires those permissions._