add note on breaking changes

README.md

@@ -5,7 +5,9 @@
 > [!WARNING]
 > **During the beta period, the master branch may be unstable**. The master
 > branch will likely include unreleased code, and may not build at all. Please
-> use the latest [release](#installation) for a stable build.
+> use the latest [release](#installation) for a stable build. In addition, we
+> may introduce breaking API changes during the beta, but we will do our best
+> to provide automated migrations when possible.
 
 > [!NOTE]
 > **During the beta, your feedback is greatly appreciated!** We'd love to hear