Add OpenSign™

[nxglabs]

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

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[Ki-er]

Please also remove the comments.

[Ki-er]

https://github.com/OpenSignLabs/OpenSign/releases/tag/v1.0.1

First release was 1 month ago. Please resubmit when this is more than 4 months old.

To be revisited 3 March 2024

[nxglabs]

@Ki-er now that the project is more than 4 months old, please add it.

[Ki-er]

Some changes to be made.

[Ki-er]

Looks good to me!