Publish instructions for Dart Dev Compiler

There are the steps for developers on the Dart Dev Compiler team to publish a new version to pub. The edit steps can be done directly on github if preferred.

Obtain permission

If you have not uploaded before, you may need to ask an existing uploader to grant you permission. They'll need to run:

> pub uploader add <your-email-address>

Update the version number

Update the following files with the new version number:

Update the Changelog

Update with notable changes since the last release.

Update your local master

Make sure the above is committed to github master. Make sure you have those updates in your local master:

> git pull

Tag the new version locally

> git tag <new-version-number> # E.g., git tag 0.1.14

Push the tag

> git push --tags

Check the github site to make sure the tag appears there under the Branch button.

Publish the new version to pub

> pub lish

Check to ensure the latest DDC is there.