add stable diffusion to API docs (keras-team#1093)

Author: LukeWood

scripts/cv_api_master.py

@@ -197,6 +197,13 @@
     "title": "Models",
     "toc": True,
     "children": [
+        {
+            "path": "stablediffusion",
+            "title": "The StableDiffusion model",
+            "generate": [
+                "keras_cv.models.StableDiffusion",
+            ],
+        },
         {
             "path": "retinanet",
             "title": "The RetinaNet model",