[Gardening] Clarify SILOptions flag docs.

Specifically, those pertaining to lifetime completion.

Author: nate-chandler

include/swift/AST/SILOptions.h

@@ -188,10 +188,10 @@ class SILOptions {
   /// If set to true, compile with the SIL Opaque Values enabled.
   bool EnableSILOpaqueValues = false;
 
-  /// Require linear OSSA lifetimes after SILGen
+  /// Introduce linear OSSA lifetimes after SILGen
   bool OSSACompleteLifetimes = false;
 
-  /// Verify linear OSSA lifetimes after SILGen
+  /// Verify linear OSSA lifetimes throughout OSSA pipeline.
   bool OSSAVerifyComplete = false;
 
   /// Enable pack metadata stack "promotion".