fix(virtual-backgrounds) add segmentation model license information

Fixes: https://github.com/jitsi/jitsi-meet/issues/8792

react/features/stream-effects/virtual-background/vendor/README.md

 More details:
 - [WebAssembly](https://webassembly.org/)
 - [WebAssembly SIMD](https://github.com/WebAssembly/simd)
-- [TFLite](https://blog.tensorflow.org/2020/07/accelerating-tensorflow-lite-xnnpack-integration.html)
+- [TFLite](https://blog.tensorflow.org/2020/07/accelerating-tensorflow-lite-xnnpack-integration.html)
+
+## LICENSE
+
+The mdoels vendored here were downloaded early January (they were available as early as the 4th), before Google switched the license away from Apache 2. Thus we understand they are not covered by the new license which according to the [model card](https://drive.google.com/file/d/1lnP1bRi9CSqQQXUHa13159vLELYDgDu0/view) dates from the 21st of January.
+
+We are not lawyers so do get legal advise if in doubt.
+
+References:
+
+- Model license discussion: https://github.com/tensorflow/tfjs/issues/4177
+- Current vendored model is discovered: https://github.com/tensorflow/tfjs/issues/4177#issuecomment-753934631
+- License change is noticed: https://github.com/tensorflow/tfjs/issues/4177#issuecomment-771536641