Mighty does not support printing or adding your local printers. We understand this is an important feature to many users and it's on our list of tasks to work on.
For now, the best alternative to printing within Mighty is to print/save your page as a PDF to download to your local host and then print it out. To print a web page to a PDF, hit command + P on your desired web page. The prompt will allow you to Save as PDF and it will download to your local machine. From there, open the PDF file and print as your normally would any regular file.
If this is an important workflow for you in Mighty please reach out and let us know so we can better prioritize this issue.