Breadcrumbs to the wiki (#5017)

* Breadcrumbs to the wiki

* Update README.md

CONTRIBUTING.md

@@ -207,7 +207,8 @@ find . -mindepth 1 -maxdepth 1 -type d | xargs -n 1 sh -c 'ninja -C $0 || exit 2
 Contributing code
 -----------------
 
-We gladly accept contributions via GitHub pull requests.
+We gladly accept contributions via GitHub pull requests. See [the wiki](https://github.com/flutter/engine/wiki) for
+information about the engine's architecture.
 
 To start working on a patch:
 

README.md

@@ -28,6 +28,9 @@ us [feedback](mailto:flutter-dev@googlegroups.com).
 
  - For information about contributing code to the engine itself, please see
    [CONTRIBUTING.md](CONTRIBUTING.md).
+   
+ - For information about the engine's architecture, please see
+   [the wiki](https://github.com/flutter/engine/wiki).
 
 Community
 ---------