The instruction of the README in the root directory is out of date

[ErkangXu]

• [x] I have searched the issues of this repository and believe that this is not a duplicate.

Describe the proposal

The instruction was written at the time when the dubble-samples-api runs with multicast registry. But now it requires zookeeper registry started first. We should update the instruction to give new comer a better first impression.

[AlbumenJ]

Agree. Readme is too too too old now~