hbase-store: add comments
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yangwenmai/tidb,astaxie/tidb,kyle-wang/tidb,ueizhou/tidb,ngaut/tidb,pingcap/tidb,mccxj/tidb,pingcap/tidb,Nify/tidb,myrice/tidb,coocood/tidb,louishust/tidb,louishust/tidb,c4pt0r/tidb,kyle-wang/tidb,simon-xia/tidb,zs634134578/tidb,c4pt0r/tidb,zs634134578/tidb,pingcap/tidb,zimulala/tidb,yuanwhy/tidb,8cbx/tidb,wusphinx/tidb,kyle-wang/tidb,kyle-wang/tidb,anywhy/tidb,ngaut/tidb,Cofyc/tidb,JinheLin/tidb,yangwenmai/tidb,EvilMcJerkface/tidb,astaxie/tidb,ngaut/tidb,silenceper/tidb,ming-relax/tidb,simon-xia/tidb,liyu4/tidb,c4pt0r/tidb,spongedu/tidb,XuHuaiyu/tidb,gaocegege/tidb,ueizhou/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,mccxj/tidb,zimulala/tidb,cosmtrek/tidb,qhsong/tidb,tiancaiamao/tidb,tiancaiamao/tidb,pingcap/tidb,JinheLin/tidb,silentred/tidb,8cbx/tidb,cosmtrek/tidb,Cofyc/tidb,ming-relax/tidb,ngaut/tidb,myrice/tidb,wusphinx/tidb,qiuyesuifeng/tidb,liyu4/tidb,CodeRushing/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,spongedu/tidb,EvilMcJerkface/tidb,XuHuaiyu/tidb,ngaut/tidb,yuanwhy/tidb,gaocegege/tidb,anywhy/tidb,silentred/tidb,silenceper/tidb,Nify/tidb,kyle-wang/tidb,qhsong/tidb,andelf/tidb,andelf/tidb,CodeRushing/tidb,qiuyesuifeng/tidb,coocood/tidb,c4pt0r/tidb