Add information how to use library

[cornelius]

It could be helpful to add some information for developers how to use specific libraries, e.g. how to include them in their projects, how to link to them, etc. An example of what information that could be can be seen on the KDE API documentation (look at the left column of e.g. the Karchive API docs).

It could be just an (optional) link to a web page describing how to use the library. But maybe it would be helpful to codify how to use the library in a stricter way, so it would become possible to automatically add qmake statements or things like that. Needs a bit of thought.