Create better website dev documentation

[mririgoyen]

As a potential contributor to the Pictogrammers website, I would like to know about how to get started, technologies used, file structure, acceptable coding practices, etc., so that if I create a PR, it can be reviewed and merged quickly.

AC:

• [ ] Write new/update existing documentation in the Contribute to the Pictogrammers Website doc.
• [x] Link to this document in the README in the root of this repo.