Update github user reference

[alexis-opolka]

Description

GitHub doesn't link usernames in the README, if we want to reference the user it should be as a link.

My Pull Request only modifies this tiny bit in the README.

Motivation and Context

I just want others to be able to land on Rikj000's profile page on GitHub.

How Has This Been Tested?

N/A

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[yubiuser]

Thanks for your contribution. Please target development-v6 branch, squash your commits down and sign them off. See https://docs.pi-hole.net/guides/github/dco/

[alexis-opolka]

It should be good now, my branch should be in accord with the targeted development-v6 branch and only one commit, now signed, should appear.