updated README.md with a note about Zynq clock configuration
updated README.md with a note about Zynq clock configuration

chenm001/connectal,csail-csg/connectal,8l/connectal,chenm001/connectal,hanw/connectal,cambridgehackers/connectal,chenm001/connectal,cambridgehackers/connectal,csail-csg/connectal,hanw/connectal,8l/connectal,csail-csg/connectal,chenm001/connectal,8l/connectal,csail-csg/connectal,hanw/connectal,8l/connectal,chenm001/connectal,cambridgehackers/connectal,cambridgehackers/connectal,hanw/connectal,cambridgehackers/connectal,csail-csg/connectal,8l/connectal,hanw/connectal