Another wait_for_yellow to the docs

All in service of the snippets passing consistently.

docs/reference/mapping/params/analyzer.asciidoc

@@ -60,6 +60,8 @@ PUT my_index
   }
 }
 
+GET _cluster/health?wait_for_status=yellow
+
 GET my_index/_analyze?field=text <3>
 {
   "text": "The quick Brown Foxes."