docs changes to Cfg key concepts
docs changes to Cfg key concepts

steveyen/cbft,couchbaselabs/cbft,nimishzynga/cbgt,couchbaselabs/cbft,couchbaselabs/cbgt,steveyen/cbft,steveyen/cbft,nimishzynga/cbgt,steveyen/cbft,couchbaselabs/cbgt,couchbaselabs/cbft,nimishzynga/cbgt,nimishzynga/cbgt,couchbaselabs/cbgt,steveyen/cbft,couchbaselabs/cbft,couchbaselabs/cbgt