Update each example with authentication details.

Each example's module comment should include a short note about the authentication method. These samples use implicit authentication through environment variables. The comment should point to the README, and the README should link to the LoginRunner example and the public documentation where authentication is discussed.

Locate each example's module comment and the README, then review the LoginRunner example and the public documentation covering authentication. Add the requested implicit environment-variable authentication note and links; done means every example comment points to the README, and the README links to LoginRunner and the authentication documentation.

Written by the indexing model from the issue text.