openshiftGH-53958: Fix xref guidelines for contrib doc

As called out in the comments: openshift#53958

This updates the `/baz/zig` and `/baz/zag` examples.

@openshift/team-documentation PTAL

contributing_to_docs/doc_guidelines.adoc

@@ -758,8 +758,8 @@ The following examples use the example directory structure shown here:
 /foo
 /foo/bar.adoc
 /baz
-/baz/zig.adoc
-/baz/zag.adoc
+xref:../baz/zig.adoc
+xref:../baz/zag.adoc
 ....
 
 *Link to assembly in same directory*