Fixed some typos in the top-level README
Fixed some typos in the top-level README

jcowles/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,c64kernal/OpenSubdiv,poljere/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,c64kernal/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv,lookup1980/OpenSubdiv,xldeveloper/OpenSubdiv,nyotis/OpenSubdiv,shengfuintel/OpenSubdiv,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,shengfuintel/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,jcowles/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,c64kernal/OpenSubdiv,jcowles/OpenSubdiv,lookup1980/OpenSubdiv,lookup1980/OpenSubdiv,xldeveloper/OpenSubdiv,anshuarya/OpenSubdiv