Add documentation to get a Drush uli link in the Tugboat terminal

[dacharyc]

@YesCT shared a code snippet for creating a custom Drush config to create a nice Drush uli link in the Tugboat terminal:

Add this to the /.tugboat/config.yml:

# Use custom drush config. 
cp "${TUGBOAT_ROOT}/.tugboat/drush.yml" "${TUGBOAT_ROOT}/drush"

Then create a custom Drush config - for example /.tugboat/drush.yml, containing this:

options: 
     uri: ${env.TUGBOAT_DEFAULT_SERVICE_URL}

Consider whether this belongs in the docs. Possible places include:

• In the Drupal tutorial documents
• Possible "community snippets" as a companion to the "community images" page