Update PMDK sub-page in Developer Hub

[lukaszstolarczuk]

We may, most likely, want to update the Developer Hub, to avoid looking for, e.g., 'RPMA' within PMDK section. I believe we should have a separate section for all repositories independent from PMDK repository.

Some of the descriptions within the PMDK page should probably be also updated with more/up-to-date content.

Perhaps repositories that will move out (to a separate sub-page with a link in Dveloper Hub) should be removed or just clearly stated that they are not part of the PMDK repo (links for backward compatibility would be nice - there is a possibility to specify
a link to a section within PMDK web page).

[lukaszstolarczuk]

This issue includes creating at least a separate link (in Developer Hub) to RPMA project (which is now an independent project and will even work without libpmem).