Add link to the pitch thread in the 'Member import visibility proposal'.

Author: tshortli

proposals/NNNN-member-import-visibility.md

@@ -7,7 +7,7 @@
 * Bug: [apple/swift#46493](https://github.com/apple/swift/issues/46493)
 * Implementation: [apple/swift#72974](https://github.com/apple/swift/pull/72974), [apple/swift#73063](https://github.com/apple/swift/pull/73063)
 * Upcoming Feature Flag: `MemberImportVisibility`
-* Review: TBD
+* Pitch: [Forum Thread](https://forums.swift.org/t/pitch-fixing-member-import-visibility/71432)
 
 ## Introduction
 
@@ -146,4 +146,4 @@ One alternative approach to the problem would be to rely exclusively on a new sy
 
 ## Acknowledgments
 
-I would like to thank Doug Gregor for providing a proof-of-concept implementation of this pitch.
+I would like to thank Doug Gregor for providing a proof-of-concept implementation of this pitch.