fix typo on getting started
fix typo on getting started

SteamShon/incubator-s2graph,daewon/incubator-s2graph,daewon/incubator-s2graph,jongwook/incubator-s2graph,jongwook/incubator-s2graph,SteamShon/incubator-s2graph,SteamShon/incubator-s2graph