Clarify banner on main docs page

Author: SS-JIA

docs/source/index.rst

@@ -4,7 +4,7 @@ Welcome to the ExecuTorch Documentation
 =======================================
 
 .. important::
-   v0.4.0 is a beta release of ExecuTorch. As of this release, the API will
+   v0.4.0 is the beta release of ExecuTorch. As of v0.4.0, the API will
    follow the `API Lifecycle and Deprecation Policy <api-life-cycle.html>`__,
    and the ``.pte`` binary format will comply with the `Runtime Compatibility
    Policy