* I cretaed a folder 'development'
* I split up the file dev.md into three parts and moved it to this folder
* index.md
* authentication_authorization.md
* mrf.md
* I also moved ap_extensions.md
* I created a new file setting_up_pleroma_dev.md
Added ffmpeg/imagemagick checks to launch checks (if media preview proxy is enabled). Added documentation on installing optional media / graphics packages (imagemagick, ffmpeg, exiftool).
Ilja