Add Mermaid Support

[jrg94]

This is a massive stretch goal, but we could theoretically include a mermaid template. Of course, the user can already do this using the Code block, but it would be cool to allow them to create the object relationships programmatically. I just had no clue that GitHub would render mermaid diagrams as seen here: https://github.com/gbshp/Project-portfolio/pull/2/files#diff-9e2e48ceb12e233a8acd23dafab8c74fc723f2ec1463981fcb6ca740ffd799f4