Updated README to be more concise
Updated README to be more concise

The main README should:
1) Reflect the goal of the project
2) Provide a link to the documentation hub
3) Provide a link to the issue hub
ericchang/incubator-toree,asorianostratio/incubator-toree,lresende/incubator-toree,Myllyenko/incubator-toree,asorianostratio/incubator-toree,kapil-malik/incubator-toree,poplav/incubator-toree,poplav/incubator-toree,kapil-malik/incubator-toree,asorianostratio/incubator-toree,lresende/incubator-toree,kapil-malik/incubator-toree,hmost1/incubator-toree,hmost1/incubator-toree,chipsenkbeil/incubator-toree,Myllyenko/incubator-toree,apache/incubator-toree,mariusvniekerk/incubator-toree,kapil-malik/incubator-toree,asorianostratio/incubator-toree,chipsenkbeil/incubator-toree,poplav/incubator-toree,ericchang/incubator-toree,hmost1/incubator-toree,Myllyenko/incubator-toree,chipsenkbeil/incubator-toree,mariusvniekerk/incubator-toree,apache/incubator-toree,slowenthal/spark-kernel,poplav/incubator-toree,lresende/incubator-toree,poplav/incubator-toree,kapil-malik/incubator-toree,lresende/incubator-toree,Myllyenko/incubator-toree,mariusvniekerk/incubator-toree,mariusvniekerk/incubator-toree,ericchang/incubator-toree,chipsenkbeil/incubator-toree,hmost1/incubator-toree,ericchang/incubator-toree,apache/incubator-toree,ericchang/incubator-toree