(re-)add clink

[crueter]

Signed-off-by: swurl swurl@swurl.xyz

Thanks for taking the time to suggest an addition to awesome-selfhosted!

To ensure your Pull Request is dealt with swiftly, please check the following (check the boxes [x]):

• Submit one item per pull request. This eases reviewing and speeds up inclusion.
• You have searched the repository for any relevant issues or PRs, including closed ones.
• Any software you are adding is not already listed at any of awesome-sysadmin, staticgen.com, staticsitegenerators.net, dbdb.io.
• The file you are adding is formatted as described in addition.md.
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clink was previously removed due to an expired certificate and a belief that it's unmaintained. However, clink is still actively maintained--it hasn't received updates because it doesn't need any--and certificate renewal automation has been fixed.

See also #1171 for more info on cert conflicts/maintenance.