Added an ER Diagram of Database Schema

[murtazahatim]

What Added pdf ER diagram of the mongodb database

Description Added the ER diagram of the db schema in Trellis/db_documentation/database_ER_diagram.pdf

Fixes # (issue reference)

38

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update
• [x] Documentation update

Checklist

• [x] I have read the Contribution Guidelines
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review
• [x] My changes generate no new warnings

Expected Outcome

[ayushagg31]

Looks great, couldn't have done better myself. Although there's few minor issues I would like you to work on-

• What does NN signify in your ERD?
• Connect board.image with board schema (maybe an upward connecting arrow will do)
• Remove color section from board schema
• Change it to img format, instead of pdf, so we can add this to readme
• Don't create new folder for ERD, add it to root with title ERD.png.

Rest looks good, thanks 👍.

[murtazahatim]

@ayushagg31 The only change I was unable to make is: Remove color section from board schema

as the software I am using automatically adds that since it is linked to board.image. Hence, I added all three fields of board.image to make it uniform. Hope this is okay.