Added R74n to sites.yml

[slweeb]

Website (if applicable): https://r74n.com

This PR is:

• [x] Adding a new domain

• [ ] Updating existing domain

• [ ] Changing domain name

• [ ] Removing existing domain from list

• [ ] Website code changes (darktheme.club site)

• [ ] Other not listed

• [x] The following information is filled identical to the data file

I confirm that I have read the FAQ page, particularly the red section about inappropriate content, and I attest that this site is appropriate based on those criteria.

• [x] Check to confirm

- domain: r74n.com
  url: https://r74n.com/
  method: darkonly
  last_checked: 2024-03-20

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[garritfra]

Thanks!