Fix API Stylebook link

[br-tyler-milner]

Fix link to https://apistylebook.stoplight.io in readme.

Motivation and Context

API Stylebook link at bottom of readme attempts to load a page within GitHub (see screenshot).

Description

Added https:// to API Stylebook link.

How Has This Been Tested?

Clicking API Stylebook link in readme on my fork loads the page correctly now.

Screenshot(s)/recordings(s)

Types of changes

• 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 change)

Checklist

• This PR's code follows as closely as possible the coding style/guidelines of this project.
• I have added error reporting and followed the error reporting guidelines.
• I have added event tracking and followed the event tracking guidelines.
• I have updated any relevant documentation accordingly to reflect this PR's changes.
• I have added automated tests (unit/integration/e2e/other) to cover my changes.
• All new and existing tests pass locally (excluding flaky CI tests).