doc(README.md): Add pkg-config-path for clp-1.17
doc(README.md): Add pkg-config-path for clp-1.17

soonho-tri/dreal4,dreal/dreal4,dreal/dreal4,dreal/dreal4,dreal/dreal4,soonho-tri/dreal4,soonho-tri/dreal4,soonho-tri/dreal4