Update installation.md
Update installation.md

Added build instructions for OpenCL support.

Added instructions for getting the OpenCL ICD.

kaiping/incubator-singa,nusdbsystem/incubator-singa,apache/incubator-singa,wangsheng1001/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,nudles/incubator-singa,ijingo/incubator-singa,apache/incubator-singa,nusdbsystem/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,nusdbsystem/incubator-singa,wangsheng1001/incubator-singa,nudles/incubator-singa,nusdbsystem/incubator-singa,nudles/incubator-singa,wangsheng1001/incubator-singa,nudles/incubator-singa,nusdbsystem/incubator-singa,ijingo/incubator-singa,nudles/incubator-singa,wangsheng1001/incubator-singa,ijingo/incubator-singa,kaiping/incubator-singa,ijingo/incubator-singa,kaiping/incubator-singa,wangsheng1001/incubator-singa,apache/incubator-singa,ijingo/incubator-singa