suggest orphan PRs labelling procedure

Author: Ivansete-status

PROCESS.md

@@ -122,7 +122,7 @@ A _Deliverable_:
   - dogfooding
   - docs
 
-Finally, for _Tasks_ that do not belong to a _Deliverable_:
+Finally, for _Tasks_ or _PRs_ that do not belong to a _Deliverable_:
 - MUST qualify either as (with related GitHub labels):
   - `bug`: bugs reported by users or discovered internally, SHOULD be linked back to a corresponding _FURPS_ and _Milestone_.
   - `test`: maintaining and fixing broken tests, SHOULD ideally be linked back to a corresponding _FURPS_ and _Milestone_.