add link to contrib guide building steps in readme
add link to contrib guide building steps in readme

mhelmetag/exercism.io,tejasbubane/exercism.io,mhelmetag/exercism.io,treiff/exercism.io,RaptorRCX/exercism.io,treiff/exercism.io,nathanbwright/exercism.io,mhelmetag/exercism.io,jtigger/exercism.io,treiff/exercism.io,tejasbubane/exercism.io,nathanbwright/exercism.io,jtigger/exercism.io,nathanbwright/exercism.io,RaptorRCX/exercism.io,jtigger/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,mhelmetag/exercism.io,tejasbubane/exercism.io,jtigger/exercism.io,RaptorRCX/exercism.io,treiff/exercism.io,nathanbwright/exercism.io