With the new architecture of El Capitan and Photos the developers of the 3rd party editors must provide updates to their apps with extensions that can be added so the apps can be used from within Photos. Adobe hasn't released updates or extensions so far.
Currently there are 6 apps that offer extensions to work with Photos and they must be purchase from the App store:
Intensify
BeFunky Express
Tonality
Noiseless
Snapheal
Affinity Photo.
So to use your current Photoshop with Photos export the original file to the desktop and edit it from there. When the editing is completed save and import the new file into the library.