:whale: Work about Docker. add mysql dockerfile

doc/db/Dockerfile

@@ -1,5 +1,5 @@
 FROM mysql:5.7
 MAINTAINER lengleng(wangiegie@gmail.com)
-COPY 1schema.sql /docker-entrypoint-initdb.d
-COPY 2pigxx.sql /docker-entrypoint-initdb.d
-COPY 3pigxx_ac.sql /docker-entrypoint-initdb.d
+COPY ./doc/db/1schema.sql /docker-entrypoint-initdb.d
+COPY ./doc/db/2pigxx.sql /docker-entrypoint-initdb.d
+COPY ./doc/db/3pigxx_ac.sql /docker-entrypoint-initdb.d