[README] update for v0.4b

README.md

@@ -23,6 +23,7 @@ Please see the [Getting Started](https://finn.readthedocs.io/en/latest/getting_s
 
 ## What's New in FINN?
 
+* **2020-09-21:** v0.4b (beta) is released. Read more on the <a href="https://xilinx.github.io/finn/2020/09/21/finn-v04b-beta-is-released.html">release blog post</a>.
 * **2020-05-08:** v0.3b (beta) is released, with initial support for convolutions, parallel transformations, more flexible memory allocation for MVAUs, throughput testing and many other smaller improvements and bugfixes. Read more on the <a href="https://xilinx.github.io/finn/2020/05/08/finn-v03b-beta-is-released.html">release blog post</a>.
 * **2020-04-15:** FINN v0.2.1b (beta): use fixed commit versions for dependency repos, otherwise identical to 0.2b
 * **2020-02-28:** FINN v0.2b (beta) is released, which is a clean-slate reimplementation of the framework. Currently only fully-connected networks are supported for the end-to-end flow. Please see the release blog post for a summary of the key features.