README: Add note on first run taking time (#14)

Author: stanislavkozlovski

README.md

@@ -147,6 +147,9 @@ cd /path/to/repo
 dclaude # or dcodex
 ```
 
+> [!NOTE]
+> The very first `dcodex`/`dclaude` run can take around 60 seconds while Docker builds the image. Subsequent runs are instant.
+
 If you want GitHub SSH access from inside the container, for example to `git push` from there, launch with `--ssh`:
 
 ```bash