address more caveats in oberon.ctags

oberon.ctags

@@ -24,10 +24,15 @@
 # sometimes resolve to an incorrect module. that is to say putting cursor on 
 # W in Platform.Write and jumping will probably not work as expected, so you
 # might have to do some of these
+#   add this to yout .vimrc
 #       autocmd FileType oberon,modula2 setlocal iskeyword+=.
-#   select the name fully
+#   select the qualified name
 #       v 3e <C-]>
 #       :ta Platform.Write
 #   resolve ambiguities interactively
 #       :ts Write
 #       g <C-]>
+#
+# if you need upward searching for tags file, so you can access them from
+# project root subdirectories, then add this to your .vimrc
+#   set tags=./tags;~