Update the OKH reference on the IoPA website

[hoijui]

See https://www.internetofproduction.org/openknowhow.

We should probably do that when it stabilizes a bit.

[timmwille]

I collected a few things here, we could just transfer to this OKH issue:
https://codeberg.org/OSEGermany/OpenSearchEcosystem/issues/26

@touchthesun