Summary:
This diff changes the way on how plugin documentation is produced. Instead of keeping plugin documentation together with other docs, we will now keep it together with plugin code. There are multiple advantages of such solution:
1. We are generating docs for every plugin in a standartised way so all of them looks similar. We can also use plugin metadata for generation as well (e.g. take title, icon, oncall name etc from package.json).
2. Standartised plugin docs make it possible to build docs both for websites (public and internal) and for embedding into Flipper.
3. It will hopefully incentivise authors to write docs as they will be a part of plugin "package".
4. We can scaffold documentation template using scarf to further incentivise filling it.
Reviewed By: jknoxville
Differential Revision: D29378053
fbshipit-source-id: 66ea48dc9ba225fabfb256ae6a10f8c81eef6f5f
