Add link check workflow action file

[kylmcgr]

Introduction

https://github.com/agencyenterprise/neurotechdevkit/issues/143 Adds an action to CI to check for broken links in markdown files in our repo.

[codecov-commenter]

Codecov Report

Patch has no changes to coverable lines.

:exclamation: Current head 42fa3de differs from pull request most recent head 821c34c. Consider uploading reports for the commit 821c34c to get more accurate results

:loudspeaker: Thoughts on this report? Let us know!.

[d-lucena]

Awesome, thanks @kylmcgr