Update Readme

Signed-off-by: Jorge Maidana <jorgem.seq@gmail.com>

Author: jorgem-seq

README.md

@@ -5,3 +5,4 @@ ExtIO wrapper for librtlsdr.
 * Original code from [**josemariaaraujo/ExtIO_RTL**](https://github.com/josemariaaraujo/ExtIO_RTL)
 * 03-2020: Fix line endings in files, remove unneeded code and files.
 * 12-2020: Fix mem leak, fix UB, add U8 format, add Mingw-w64 Makefiles.
+* 11-2021: Add Bias Tee option, add branch auto switch.