Error: Could not find or load main class dummy.DummyMain

**Describe the bug**

when I try to make demo, the dummy docker cannot start, it shows
Error: Could not find or load main class dummy.DummyMain

**To Reproduce**
1, clone the proj
2, cd demo
3, make compile
4, make build
5, make conf
6, make start

**Expected behavior**
something we could play with, as a starter?

maybe we could have a step guide on the main markdown?
