Document the Velocity plugin JSON file format #731
Description
The annotation processor, which is currently recommended to be used, is not exactly the nicest to use for anything slightly more dynamic (since variable substitution is hard). For this reason, we should document the Velocity plugin JSON file in order to make the manual inclusion possible.
I also think we should remove (or at least inline) any mentions of the AP for generating that file and instead make manually writing the file the preferred way.