Enhance documentation for yarn.resourcemanager.scheduler.class property

http://hadoop.apache.org/docs/r3.0.0-alpha1/hadoop-project-dist/hadoop-common/ClusterSetup.html refers to FairScheduler, when it documents the setting yarn.resourcemanager.scheduler.class. What it forgets to mention is that the user has to specify the full class path like org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FairScheduler otherwise the system throws java.lang.ClassNotFoundException: FairScheduler. It would be nice, if the documentation specified the full class path, so that the user does not need to look it up.