Adding information about QLF FPGA plugin to README.md
Adding information about QLF FPGA plugin to README.md

Signed-off-by: Maciej Kurc <572803cc6e8d7bb35033942e4b03254951a2e0d6@antmicro.com>

chipsalliance/yosys-f4pga-plugins,SymbiFlow/yosys-symbiflow-plugins,SymbiFlow/yosys-symbiflow-plugins,antmicro/yosys-symbiflow-plugins,SymbiFlow/yosys-symbiflow-plugins,chipsalliance/yosys-f4pga-plugins,SymbiFlow/yosys-f4pga-plugins,SymbiFlow/yosys-f4pga-plugins,antmicro/yosys-symbiflow-plugins,antmicro/yosys-symbiflow-plugins,SymbiFlow/yosys-f4pga-plugins