README: update dwebp help output after 1e595fe
README: update dwebp help output after 1e595fe

-scale -> -resize

Change-Id: I896f87134288099cc774c2471b9a81e7919ae045

redengineer/libwebp,Aexyn/libwebp,zofuthan/libwebp,zofuthan/libwebp,PKRoma/libwebp,Aexyn/libwebp,PKRoma/libwebp,webmproject/libwebp,zofuthan/libwebp,Aexyn/libwebp,ttyangf/libwebp,imazen/libwebp,ttyangf/libwebp,redengineer/libwebp,webmproject/libwebp,yohunl/libwebp,imazen/libwebp,redengineer/libwebp,ttyangf/libwebp,ttyangf/libwebp,Aexyn/libwebp,Aexyn/libwebp,zofuthan/libwebp,PKRoma/libwebp,PKRoma/libwebp,zofuthan/libwebp,imazen/libwebp,ttyangf/libwebp,redengineer/libwebp,PKRoma/libwebp,yohunl/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,yohunl/libwebp,redengineer/libwebp,webmproject/libwebp,imazen/libwebp,yohunl/libwebp,imazen/libwebp,yohunl/libwebp