Include an optional node "baseURL" in entity.letterhead to help construct templates that refer to resources located at a common base path. These could be images, HTML, plain text etc.
While not currently used in templates, this is designed for resources that are publicly accessible via a website.
It would typically be used for email templates to generate links to images (as images cannot be reliably be included directly due to the way different email clients support them).
When populating the field, it should always containing a trailing slash e.g. https://vetsrus.com/resources/