add usage information for individual values

[dret]

there should be a way how data can be added that talks about how individual concept values are used in concrete services: it would be something along the lines of being able to say, "API X uses HTTP request method GET and HTTP status codes 200 and 404."
This has been discussed with @mitraman and @RubenVerborgh and it would be great to get some feedback or even use cases from them. for now, the simple assumption is that this data would be a useful way to link back from web concepts to concrete APIs, and thus could turn web concepts into a useful discovery tool of an existing API landscape, if the usage data for that landscape is fed into web concepts.
for the "original" web concepts repo and site, this probably does not even matter. but any fork might benefit from this if the fork could be easily turned into an overview page for an existing landscape of APIs (driven by the usage data for these specific APIs).