Add warning about on-going re-write in main branch

README.md

@@ -1,3 +1,5 @@
+**Warning: This theme is going through a heavy re-write. The `main` branch contains some undocumented changes. Please, do not use `main` branch. Use latest release instead. We will release a new version once the re-write is done and the changes are documented.**
+
 # Toha
 
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