vl_fisher.c: doc: add two options
vl_fisher.c: doc: add two options

cvfish/vlfeat,WangDequan/vlfeat,mylxiaoyi/vlfeat,CansenJIANG/vlfeat,cvfish/vlfeat,erexhepa/vlfeat,vlfeat/vlfeat,CansenJIANG/vlfeat,hongzhili/vlfeat,j-bo/vlfeat,j-bo/vlfeat,cvfish/vlfeat,WangDequan/vlfeat,CansenJIANG/vlfeat,erexhepa/vlfeat,hongzhili/vlfeat,cvfish/vlfeat,rxl194/vlfeat,richarddzh/vlfeat,erexhepa/vlfeat,qubick/vlfeat,CansenJIANG/vlfeat,qubick/vlfeat,vlfeat/vlfeat,mylxiaoyi/vlfeat,hongzhili/vlfeat,richarddzh/vlfeat,mylxiaoyi/vlfeat,rxl194/vlfeat,erexhepa/vlfeat,cvfish/vlfeat,vlfeat/vlfeat,hongzhili/vlfeat,mylxiaoyi/vlfeat,rxl194/vlfeat,rxl194/vlfeat,rxl194/vlfeat,qubick/vlfeat,CansenJIANG/vlfeat,rxl194/vlfeat,mylxiaoyi/vlfeat,WangDequan/vlfeat,vlfeat/vlfeat,qubick/vlfeat,hongzhili/vlfeat,cvfish/vlfeat,CansenJIANG/vlfeat,richarddzh/vlfeat,qubick/vlfeat,richarddzh/vlfeat,j-bo/vlfeat,erexhepa/vlfeat,WangDequan/vlfeat,erexhepa/vlfeat,qubick/vlfeat,vlfeat/vlfeat,vlfeat/vlfeat,richarddzh/vlfeat,hongzhili/vlfeat,j-bo/vlfeat,WangDequan/vlfeat,WangDequan/vlfeat,j-bo/vlfeat,mylxiaoyi/vlfeat,richarddzh/vlfeat