Documentation: Added tutorial for creating a custom spinner

[jordancolbeth]

Description of new feature, or changes

This PR adds a new directory called "tutorials", and inside that is a PDF written tutorial that goes over how to create a user's first custom spinner (this is for beginner users and people with little experience in software). It uses the custom_spins.py example program as a base to work off and explains each piece of the program and how to get it running on the user's machine.

Checklist

• [x] Your branch is up-to-date with the base branch
• [n/a] You've included at least one test if this is a new feature
• [n/a] All tests are passing

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