Add notes about current development status and breaking changes (#93)

Author: brichet

README.md

@@ -10,6 +10,11 @@ Many components of this chat project come from [jupyter-ai](https://github.com/j
 
 ![a screenshot showing the jupyter-chat extension used in two browser windows](https://github.com/jupyterlab/jupyter-chat/assets/591645/5dac0b00-43ed-4458-ab67-18207644b92b)
 
+> **Warning**
+>
+> This project is still in early development stage and its API may change often before
+a stable release.
+
 ## Composition
 
 ### Typescript package

docs/source/developers/index.md

@@ -5,6 +5,11 @@ This section is aimed at developers and contains documentation on :
 - how to develop a chat extension or include one of the chat extensions
 - how to contribute to this project
 
+```{warning}
+This project is still in early development stage and its API may change often before a
+stable release.
+```
+
 ```{toctree}
 ---
 maxdepth: 2