HBASE-21606 document meta table load metrics
HBASE-21606 document meta table load metrics

Closes #369

Signed-off-by: Xu Cang <6a227875f6f467ee8679bc6c952c8607e99c44b8@apache.org>
Signed-off-by: Sakthi <d528f49be3d74e7374b15f6185529690e8eaee3d@gmail.com>
Signed-off-by: Sean Busbey <5c0191c5bda2836af1cb87878694cfbf1db676c8@apache.org>

Apache9/hbase,francisliu/hbase,ChinmaySKulkarni/hbase,mahak/hbase,apurtell/hbase,mahak/hbase,francisliu/hbase,ChinmaySKulkarni/hbase,ChinmaySKulkarni/hbase,ndimiduk/hbase,Apache9/hbase,ChinmaySKulkarni/hbase,ndimiduk/hbase,mahak/hbase,Apache9/hbase,ChinmaySKulkarni/hbase,Apache9/hbase,ChinmaySKulkarni/hbase,mahak/hbase,apurtell/hbase,apurtell/hbase,ChinmaySKulkarni/hbase,ndimiduk/hbase,mahak/hbase,ndimiduk/hbase,francisliu/hbase,francisliu/hbase,Apache9/hbase,mahak/hbase,mahak/hbase,francisliu/hbase,francisliu/hbase,francisliu/hbase,apurtell/hbase,mahak/hbase,ndimiduk/hbase,francisliu/hbase,ChinmaySKulkarni/hbase,apurtell/hbase,ndimiduk/hbase,Apache9/hbase,apurtell/hbase,mahak/hbase,apurtell/hbase,mahak/hbase,Apache9/hbase,ndimiduk/hbase,francisliu/hbase,ndimiduk/hbase,ChinmaySKulkarni/hbase,apurtell/hbase,Apache9/hbase,Apache9/hbase,ChinmaySKulkarni/hbase,ndimiduk/hbase,Apache9/hbase,francisliu/hbase,ndimiduk/hbase,apurtell/hbase,apurtell/hbase