chore(showcase): added www.prtdomingo.com to sites.yml showcase

[prtdomingo]

No description provided.

[gillkyle]

Thanks @prtdomingo! Looks nice!

[gatsbot]

Holy buckets, @prtdomingo — we just merged your PR to Gatsby! 💪💜

Gatsby is built by awesome people like you. Let us say “thanks” in two ways:

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Thanks again!

[prtdomingo]

Thanks! :)