[gardening] add missing links to PRs in change log (#3489)

Author: WowbaggersLiquidLunch

CHANGELOG.md

@@ -7,7 +7,7 @@ Swift v.Next
 
 Swift 5.5
  -----------
-* [3410]
+* [#3410]
     In a package that specifies a minimum tools version of 5.5, `@main` can now be used in a single-source file executable as long as the name of the source file isn't `main.swift`.  To work around special compiler semantics with single-file modules, SwiftPM now passes `-parse-as-library` when compiling an executable module that contains a single Swift source file whose name is not `main.swift`.
 
 * [#3310]
@@ -144,3 +144,7 @@ Swift 3.0
 [#1489]: https://github.com/apple/swift-package-manager/pull/1489
 [#1604]: https://github.com/apple/swift-package-manager/pull/1604
 [#2937]: https://github.com/apple/swift-package-manager/pull/2937
+[#3292]: https://github.com/apple/swift-package-manager/pull/3292
+[#3310]: https://github.com/apple/swift-package-manager/pull/3310
+[#3316]: https://github.com/apple/swift-package-manager/pull/3316
+[#3410]: https://github.com/apple/swift-package-manager/pull/3410