Minor update to README (#5003)

* Adds a docs directory with an architecture diagram from @chinmaygarde.
* Excludes the flutter/docs directory from license script.

README.md

@@ -6,9 +6,14 @@ Flutter is a new way to build high-performance, cross-platform mobile apps.
 Flutter is optimized for today's, and tomorrow's, mobile devices. We are
 focused on low-latency input and high frame rates on Android and iOS.
 
-The Flutter Engine is the runtime environment for hosting Flutter applications.
-Most developers will interact with Flutter via the Flutter Framework and APIs,
-which run inside the engine.
+The Flutter Engine is a portable runtime for hosting
+[Flutter](https://flutter.io) applications.  It implements Flutter's core
+libraries, including animation and graphics, file and network I/O,
+accessibility support, plugin architecture, and a Dart runtime and compile
+toolchain. Most developers wil interact with Flutter via the [Flutter
+Framework](https://github.com/flutter/flutter), which provides a modern,
+reactive framework, and a rich set of platform, layout and foundation widgets.
+
 
 _Flutter is still under development and we continue to add 
 features._ However, it is ready for use by early adopters who are willing to deal

tools/licenses/lib/main.dart

@@ -2106,6 +2106,7 @@ class RepositoryFlutterDirectory extends RepositoryDirectory {
   bool shouldRecurse(fs.IoNode entry) {
     return entry.name != 'testing'
         && entry.name != 'tools'
+        && entry.name != 'docs'
         && entry.name != 'examples'
         && entry.name != 'build'
         && entry.name != 'travis'