Fix #387 stack documentation/readme (resubmission, I broke the old one)

[itchylol742]

Description

Please describe what changes you have made.

Added documentation for the stack data structure with a readme and diagram

Fixes #387 stack documentation/readme This is a resubmission of a pull request I did before, but I broke it when I updated the master branch of my fork and couldn't fix it.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (change which fixes an issue with the algorithm)

• [ ] New Algorithm (non-breaking change which adds functionality)

• [x] Documentation

Checklist:

• [x] My change requires a change to the documentation.

• [x] I have updated the documentation accordingly.

• [x] I have read the CONTRIBUTING document.