Added script to run local files on App Engine

pkg/docgen/README.md

 docgen
 ======
 
 A documentation generator for Dart.
 - - -
 The docgen tool takes in a file or directory as input and produces documentation
 for all `.dart` file it finds as YAML or JSON files. This outputs information 
 about all classes, variables, functions, and methods defined in the library and 
 its imported libraries.
 
@@ skipping 19 matching lines @@
 
 ###### Options available
 
 - `-h`, `--help` Prints help and usage information.
 - `-v`, `--verbose` Output more logging information.
 - `-j`, `--[no-]json` Outputs to JSON. Files are outputted to YAML by default.
 - `--include-private` Flag to include private declarations.
 - `--include-sdk` Flag to parse SDK Library files imported.
 - `--parse-sdk` Parses the SDK libraries only. (Ignores the path passed in.)
 - `--package-root` Sets the package root of the library being analyzed.
+- `--append` Appends to the docs folder, library_list.txt, and index.txt.
 
 ###### Output Directory
 Documented libraries will be located at bin/docs in either YAML or JSON format 
 depending on options specified. There will also be a library_list.txt, 
 containing a list of all the libraries inside the docs folder. 
 
 To get more information on how to use the outputted documentation with 
 dartdoc-viewer, please take a look at the 
 [dartdoc-viewer documentation][dartdoc-viewer].
 
-[dartdoc-viewer]: https://github.com/dart-lang/dartdoc-viewer "Dartdoc-Viewer"
-
 #### Uploading to Cloud Storage
 
 To push new files to Google Cloud Storage for use by the viewer, use the 
 `gsutil` tool located at third_party/gsutil/gsutil in the Dart repository.
 
  - Run `python gsutil -m cp -q -a public-read -r <folder> gs://dartlang-docgen`
  to upload the specified folder to the viewer's bucket. Be sure to also upload 
  a new VERSION file if the uploaded folder is to be used.**
 
 **Note that the bucket contains several numbered folders for each version of 
 the documentation. Run `python gsutil ls gs://dartlang-docgen` to see the file 
 layout. Follow this convention and update a new VERSION file when uploading 
 a new version of documentation. You can see the format of the VERSION file 
 by running `python gsutil cat gs://dartlang-docgen/VERSION`.
+
+### Viewing Generated Documentation
+
+Docgen's generated YAML files can be used by the 
+[Dart Documentation Viewer][dartdoc-viewer] for easy viewing and navigation 
+through a project. 
+
+---
+
+#### Using dartdoc.py
+
+The `dartdoc.py` script located in the `bin` directory is a useful tool for 
+creating documentation for a Dart project and running it locally. 
+
+##### Setup
+
+The `dartdoc.py` script makes use of the 
+[Google App Engine SDK for Python][GAE]'s development server to serve the 
+documentation viewer. Install a recent version of the SDK before running 
+`dartdoc.py`.
+
+##### Running dartdoc.py
+
+######Common Options
+
+The following options are the most used:
+
+    python dartdoc.py --gae-sdk=<path to SDK>
+      --options=<path to files>
+      --options=--parse-sdk
+      --options='--include-sdk <path to files>'
+      --options='--append <path to files>'
+
+######All Options
+
+Run `python dartdoc.py -h` from the `bin` directory for all available options. 
+The two required options are as follows:
+ 
+ 1. The `--options` option describes any options being passed into `docgen.dart`.
+ If more then one option is desired, separate the options with a space 
+ (ex. `--options='--include-sdk files'`).
+ 2. The `--gae-sdk` option gives the absolute path to the 
+ [Google App Engine SDK][GAE]. 
+
+Running `python dartdoc.py --options=<docgen options> --gae-sdk=<path to SDK>` 
+will serve files generated by `docgen.dart` in your browser.
+
+[dartdoc-viewer]: https://github.com/dart-lang/dartdoc-viewer "Dartdoc-Viewer"
+[GAE]: https://developers.google.com/appengine/downloads#Google_App_Engine_SDK_for_Python  "Google App Engine SDK for Python"
+