Added documentation for observe stats
Added documentation for observe stats

Change-Id: I27a0db020e548562516f5b452aaf2c021f833a39
Reviewed-on: http://review.couchbase.org/10220
Tested-by: Dustin Sallings <1c08efb9b3965701be9d700d9a6f481f1ffec3ea@spy.net>
Reviewed-by: Dustin Sallings <1c08efb9b3965701be9d700d9a6f481f1ffec3ea@spy.net>

hisundar/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,daverigby/ep-engine,owendCB/ep-engine,jimwwalker/ep-engine,membase/ep-engine,jimwwalker/ep-engine,abhinavdangeti/ep-engine,membase/ep-engine,owendCB/ep-engine,sriganes/ep-engine,jimwwalker/ep-engine,sriganes/ep-engine,couchbaselabs/ep-engine,couchbase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,daverigby/kv_engine,sriganes/ep-engine,jimwwalker/ep-engine,hisundar/ep-engine,daverigby/kv_engine,membase/ep-engine,owendCB/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,sriganes/ep-engine,couchbaselabs/ep-engine,hisundar/ep-engine,owendCB/ep-engine,couchbaselabs/ep-engine,teligent-ru/ep-engine,daverigby/ep-engine,couchbaselabs/ep-engine,abhinavdangeti/ep-engine,abhinavdangeti/ep-engine,membase/ep-engine,daverigby/kv_engine,hisundar/ep-engine,abhinavdangeti/ep-engine,couchbaselabs/ep-engine,couchbase/ep-engine,abhinavdangeti/ep-engine,couchbase/ep-engine