Update name, link to documentation and description of PostNord API. 

Name changed form Sweden to PostNord due to PostNord is a service provider for Sweden and Denmark. 
Description adding Denmark.
Change linked documentation from from specific to general API entry point.

Update the link to the main page instead of the API directly

Meetup's REST API will stop working in winter 2021 and be replaced by their GraphQL API which is already active.