Update explanation for expect-no-warnings
Update explanation for expect-no-warnings

cliffordwolf/yosys,YosysHQ/yosys,SymbiFlow/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,SymbiFlow/yosys,SymbiFlow/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,YosysHQ/yosys,cliffordwolf/yosys,SymbiFlow/yosys,antmicro/yosys,YosysHQ/yosys,antmicro/yosys,antmicro/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,YosysHQ/yosys,SymbiFlow/yosys,antmicro/yosys