Update headings to use sentence case.

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.
 
-### Generating Files & Uploading to Cloud Storage
+### Generating files & uploading to Cloud Storage
 
 The viewer uses YAML files generated by the docgen package as the data 
 being displayed. These files are stored in Google Cloud Storage.
 
  - Run `python upload_docgen.py` to generate these files and upload them to 
  Cloud Storage as a new version.
 - - -
 These tasks can be done separately if necessary:
 
 ##### 
 
-#### Generating YAML Files
+#### Generating YAML files
 
 YAML files can be generated using the docgen package in the dart repository. 
 
 ###### Usage 
 
 Run  `dart docgen.dart [OPTIONS] <path to directory or file>`
 
 ###### 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. 
 If `--append` is used, it takes the file-format of the previous run stated in 
 library_list.json ignoring the flag.
 - `--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.json, and index.txt.
 - `--introduction` Adds the provided markdown text file as the introduction
 for the outputted documentation.
 
 
-###### Output Directory
+###### 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.json, 
 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].
 
 #### 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
+### 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 
@@ skipping 28 matching lines @@
  (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"