fix the title, clarify scope

policy/tpa-rfc-40-cymru-migration.md

 ---
-title: TPA-RFC-40: Cymru migration
+title: TPA-RFC-40: Cymru migration budget
 ---
 
 Summary: buy a few large servers to move the Cymru machines to a
@@ -125,6 +125,15 @@ The price breakdown is as follows:
 
 TODO: double-check that makes sense with the costs below.
 
+## Scope
+
+This proposal doesn't detail exactly how the migration will happen, or
+exactly where. Those two are delegated to TPA's normal decision making
+process and will probably be the subject of a new RFC detailing the
+exact hardware, providers, and migration procedures going forward.
+
+Only the budget is in question here.
+
 ## Goals
 
 No must/nice/non-goals were actually set in this proposal, because it