doc: add code review guide. (#3166)
doc: add code review guide. (#3166)


kyle-wang/tidb,EvilMcJerkface/tidb,zimulala/tidb,spongedu/tidb,8cbx/tidb,yuanwhy/tidb,zimulala/tidb,silentred/tidb,tiancaiamao/tidb,ngaut/tidb,louishust/tidb,simon-xia/tidb,Nify/tidb,yangwenmai/tidb,yangwenmai/tidb,silentred/tidb,gaocegege/tidb,anywhy/tidb,c4pt0r/tidb,pingcap/tidb,EvilMcJerkface/tidb,c4pt0r/tidb,cosmtrek/tidb,coocood/tidb,ngaut/tidb,c4pt0r/tidb,wusphinx/tidb,simon-xia/tidb,ming-relax/tidb,qiuyesuifeng/tidb,anywhy/tidb,pingcap/tidb,astaxie/tidb,XuHuaiyu/tidb,pingcap/tidb,c4pt0r/tidb,ming-relax/tidb,kyle-wang/tidb,louishust/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,mccxj/tidb,Nify/tidb,ngaut/tidb,gaocegege/tidb,kyle-wang/tidb,ngaut/tidb,ueizhou/tidb,pingcap/tidb,coocood/tidb,XuHuaiyu/tidb,CodeRushing/tidb,wusphinx/tidb,8cbx/tidb,kyle-wang/tidb,Cofyc/tidb,astaxie/tidb,CodeRushing/tidb,zs634134578/tidb,zs634134578/tidb,cosmtrek/tidb,mccxj/tidb,kyle-wang/tidb,spongedu/tidb,yuanwhy/tidb,tiancaiamao/tidb,pingcap/tidb,qiuyesuifeng/tidb,pingcap/tidb,Cofyc/tidb,ueizhou/tidb