update some doc links

Author: hannah-hyj

src/content/contribute/index.md

@@ -190,7 +190,7 @@ check out the Flutter [contribution guide][framework-contribute]
 and how to [Set up the engine development environment][engine-setup].
 
 [framework-contribute]: {{site.repo.flutter}}/blob/main/CONTRIBUTING.md
-[engine-setup]: {{site.repo.flutter}}/blob/main/engine/src/flutter/docs/contributing/Setting-up-the-Engine-development-environment.md
+[engine-setup]: {{site.repo.flutter}}/blob/main/docs/engine/contributing/Setting-up-the-Engine-development-environment.md
 
 ### Flutter packages
 

src/content/perf/faq.md

@@ -75,7 +75,7 @@ about evaluating and debugging Flutter's performance.
 * How do I query the target frames per second (of the display)?
   * [Get the display refresh rate][]
 
-[Get the display refresh rate]: {{site.repo.flutter}}/blob/main/engine/src/flutter/docs/Engine-specific-Service-Protocol-extensions.md#get-the-display-refresh-rate-_fluttergetdisplayrefreshrate
+[Get the display refresh rate]: {{site.repo.flutter}}/blob/main/docs/engine/Engine-specific-Service-Protocol-extensions.md#get-the-display-refresh-rate-_fluttergetdisplayrefreshrate
 
 * How to solve my app's poor animations caused by an expensive
   Dart async function call that is blocking the UI thread?

src/content/tools/devtools/memory.md

@@ -376,7 +376,7 @@ The quantities plotted on the y-axis are as follows:
   For more information, see [Dart VM internals][].
 
 [Command-line and server apps]: {{site.dart-site}}/server
-[Custom Flutter engine embedders]: {{site.repo.flutter}}/blob/main/engine/src/flutter/docs/Custom-Flutter-Engine-Embedders.md
+[Custom Flutter engine embedders]: {{site.repo.flutter}}/blob/main/docs/engine/Custom-Flutter-Engine-Embedders.md
 [Dart VM internals]: https://mrale.ph/dartvm/
 [DevTools Performance view]: /tools/devtools/performance
 [Flutter architectural overview]: /resources/architectural-overview