fix identation in proto3-gen.md file

4. Define a go package by appending `option go_package = "./mec0102.services.appgrantservice";`, `option go_package = "./mec0102.services.applcmservice";` or `option go_package = "./mec0102.services.apppkgmgmtservice";` in .proto files like this:

    ```Go

    ...

    syntax = "proto3";