Update CONTRIBUTING doc to mention analysis (#7277)

* Update CONTRIBUTING doc to mention analysis

* Update CONTRIBUTING.md

CONTRIBUTING.md

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 37f4394..8589ae0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -68,6 +68,27 @@
 automatically be picked when you relaunch the app.  You can do the same for your
 own code by mimicking the `pubspec.yaml` files in the `examples` subdirectories.
 
+Running the analyzer
+--------------------
+
+When editing Flutter code, it's important to check the code with the analyzer. There are two
+main ways to run it. In either case you will want to run `flutter update-packages --upgrade`
+first, or you will get version conflict issues or bogus error messages about core clases like
+Offset from `dart:ui`.
+
+For a one-off, use `flutter analyze --flutter-repo`. This uses the `.analysis_options_repo` file
+at the root of the repository for its configuration.
+
+For continuous analysis, use `flutter analyze --flutter-repo --watch`. This uses normal
+`.analysis_options` files, and they can differ from package to package.
+
+If you want to see how many members are missing dartdocs, you should use the first option,
+providing the additional command `--dartdocs`.
+
+If you omit the `--flutter-repo` option you may end up in a confusing state because that will
+assume you want to check a single package and the flutter repository has several packages.
+
+
 Running the tests
 -----------------
 
@@ -91,14 +112,14 @@
 if you built an engine in the `out/host_debug_unopt` directory, you can pass
 `--local-engine=host_debug_unopt` to run the tests in that engine.
 
-Note: Flutter tests are headless, you won't see any UI. You can use
+Flutter tests are headless, you won't see any UI. You can use
 `print` to generate console output or you can interact with the DartVM
 via observatory at [http://localhost:8181/](http://localhost:8181/).
 
 Adding a test
 -------------
 
-To add a test to the Flutter package, simply create a file whose name
+To add a test to the Flutter package, create a file whose name
 ends with `_test.dart` in the `packages/flutter/test` directory. The
 test should have a `main` function and use the `test` package.
 
@@ -107,15 +128,17 @@
 
 We gladly accept contributions via GitHub pull requests.
 
+Please peruse our
+[style guides](https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo) and
+[design principles](https://flutter.io/design-principles/) before
+working on anything non-trivial. These guidelines are intended to
+keep the code consistent and avoid common pitfalls.
+
 To start working on a patch:
 
  * `git fetch upstream`
  * `git checkout upstream/master -b name_of_your_branch`
- * Hack away. Please peruse our
- [style guides](https://flutter.io/style-guide/) and
- [design principles](https://flutter.io/design-principles/) before
- working on anything non-trivial. These guidelines are intended to
- keep the code consistent and avoid common pitfalls.
+ * Hack away.
  * `git commit -a -m "<your informative commit message>"`
  * `git push origin name_of_your_branch`