Adds note on supported openssl versions for tls certificates.

[fwh-dc]

Fixes #492

[baentsch]

Thanks for the documentation improvement, @fwh-dc !

Two nits: 1) Would you agree that underlying the whole new text with a link to https://github.com/open-quantum-safe/oqs-provider#note-on-openssl-versions would give additional context? If so, please amend the PR suitably. 2) Could you please add the tag "[skip ci]" to (any future) commits changing only documentation? The environment says Thanks (saving many CI compute cycles)

[fwh-dc]

Good point. How should I add the tag? In the commit message?

[baentsch]

Good point. How should I add the tag? In the commit message?

Yes. Simply add "[skip ci]" at the end of the commit message (without the additional "" of course).