fix "unknown model type" error when rebasing a model with API

- Add command-line model probing script for dev use
- Minor documentation tweak

scripts/probe-model.py

@@ -0,0 +1,19 @@
+#!/bin/env python
+
+import argparse
+import sys
+from pathlib import Path
+from invokeai.backend.model_management.model_probe import ModelProbe
+
+parser = argparse.ArgumentParser(description="Probe model type")
+parser.add_argument(
+    'model_path',
+    type=Path,
+)
+args=parser.parse_args()
+
+info = ModelProbe().probe(args.model_path)
+print(info)
+
+      
+