Update README about migration

README.md

@@ -1,3 +1,7 @@
+# This branch has been moved to [librespeed/speedtest-go](https://github.com/librespeed/speedtest-go). No further updates will be pushed into this branch.
+
+---
+
 ![LibreSpeed Logo](https://github.com/librespeed/speedtest/blob/master/.logo/logo3.png?raw=true)
 
 # LibreSpeed