Updated documentation to show proper usage of sheepdog_tables

This PR aims to correct an issue I ran into while trying to utilize sheepdog_tables on a fresh project. I may be missing something, but my table did not load. Some debugging revealed that the contents of the context passed to the template were not set up in the manner that the template expected. Prepending "tables." inside of the with statement fixed this issue and caused tables to display properly on the page.