README: Update README
README: Update README

* Add ZynqMP and QEMU machines to the list
* Remove Sipke as he is no longer a maintainer

Signed-off-by: Nathan Rossi <e1e6d173c6873c0ae2b831215d22380d293bb314@xilinx.com>

Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx