📦 Add linkcheck action

[TechWiz-3]

First of all, thank you for your work on this project 👍

In this PR, I have added a workflow which checks links and fails if any of them are broken.

Disclaimer: this action is my own action, the repo is here

You can view the logs of the workflow on my fork here. 3 links were found to be broken as in #32

Let me know if you'd like me to change anything, any feedback is appreciated either way :)