Modify README.md in pubsub examples to cover validation

[MregXN]

Describe

The purpose of this issue is to modify the README file of the existing pubsub examples to cover validation.

Problem

Currently, the README file provides a brief overview of how to use the examples, but it does not cover grpc part validation. What is more, if both the HTTP subscriber and the gRPC subscriber start at the same time and receive partial information published by the publisher according to the original structure, it may lead to verification errors.

Solution

• Add introduction about grpc subscribers
• Adjust introduction order to ensure complete validation without affecting each other. It is recommended to run validation in the following order: http subscriber, publisher, bulk publisher, then stop them all. Then run gRPC subscriber, publisher and bulk publisher.

[MregXN]

/assign