gistfile1.txt

/**
 * ## FooBar ViewHelper
 *
 * Blabla
 *
 * ### Argument: foo
 *
 * See: https://raw.github.com/bla/bla.md
 *
 * ### Argument: barFromParent
 *
 * Direct description, no include.
 */
class FooBarVieWHelper {

  /**
   * Init arguments
   */
  public function initializeArguments() {
    parent::initializeArguments();
    $this->registerArgument('foo', 'string', '#arg-foo', FALSE);
    $this->overrideArgument('barFromParent', 'string', '#arg-barFromParent', FALSE);
  }

}

Note. The line See: https://raw.github.com/bla/bla.md would be detected and the URL's source fetched and included upon display