chore(link): update link in command --help

[asandikci]

Link update for Accessibility

Description

Updated link https://spotdl.github.io/spotify-downloader/ to http://spotdl.rtfd.io/ in --help command.

Motivation and Context

This change increases accessibility.

How Has This Been Tested?

Just accidentally noticed link was broken then saw new link, changed link in appropriate file. Then forked project, built locally and tested if everything is okay

Screenshots (if appropriate)

Types of Changes

• small 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

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have read the CORE VALUES document
• I have added tests to cover my changes
• All new and existing tests passed

[xnetcat]

Change branch to dev