README: change mailing list from google group to lists.tidb.io (#22719)
README: change mailing list from google group to lists.tidb.io (#22719)

 
ngaut/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,ngaut/tidb,c4pt0r/tidb,pingcap/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,coocood/tidb,pingcap/tidb,coocood/tidb,kyle-wang/tidb,kyle-wang/tidb