How to include source page URL in donation page email receipt?
I think the short answer must be "no". Once the client is on a CiviCRM page, there are usually a few clicks before you get to the email receipting code, so at that point, there wouldn't be any record of the referrer (unless you have some code that is saving it). 

There should be a way to construct at least one version of a contribution page url, if you have that in your smarty variabloes, using the contribution page id, like:

https://yourdomain.org/civicrm/contribute/transact?reset=1&id={contribution page id}

There's probably a way to convert that to a wordpress shortcode if you're smarter than I am about such things.