Implement a post-commit hook that pings Read The Docs

Problem/Motivation

Updating documentation on readthedocs.org requires a manual action, unless Drupal.org implements a post-commit hook.
Some projects "fix" that by mirroring / moving their code to GitHub or Bitbucket, but that's a heavy workaround.

Drupal projects already using Read The Docs:

• Drush http://drush.readthedocs.org/en/master/
• Drupal Behat Testing http://behat-drupal-extension.readthedocs.org/en/3.0/
• Vlad http://vlad-docs.readthedocs.org/
• Paddle http://paddle.readthedocs.org/en/7.x-1.x/
• DevShop Devmaster http://devshop.readthedocs.org/en/latest/
• Hostmaster is considering #2223805: Move examples and documentation to a separate project →

Proposed resolution

Implement a post-commit hook that pings http://readthedocs.org/build/<project_name>
Documentation about that can be found at https://docs.readthedocs.org/en/latest/webhooks.html

Remaining tasks

First of all, discuss if this is wanted.

User interface changes

Allow anyone who can edit a Drupal project page to specify the Read The Docs project name. Or distract it from Resources > Documentation 'Link to the project documentation' because it will mostly contain a Read The Docs name if the documentation got rendered over there.

So we could change the text input field description from 'Link to the project documentation' to 'Link to the project documentation. If it contains readthedocs.org, a new documentation build will be triggered with each commit pushed to the default branch.'

API changes

None.