do you have one full example for lb4 app getting-started

[pailjin]

when i join you code into the application by lb4 app CLI.
some error happens.

for example:
Cannot start the application. Error: The key 'mqtt.exchange' is not bound to any value in context application
at Lb4TodoListApplication.getBinding (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/context.ts:889:11)
at Lb4TodoListApplication.getValueOrPromise (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/context.ts:953:26)
at resolution_session_1.ResolutionSession.runWithInjection.s (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/resolver.ts:155:20)
at value_promise_1.tryWithFinally (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/resolution-session.ts:149:13)
at Object.tryWithFinally (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/value-promise.ts:196:14)
at Function.runWithInjection (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/resolution-session.ts:148:12)
at resolve (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/resolver.ts:139:38)
at value_promise_1.resolveList (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/resolver.ts:241:12)
at Object.resolveList (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/value-promise.ts:168:28)
at resolveInjectedArguments (/Users/xxx/lb-4-todo-list/node_modules/@loopback/context/src/resolver.ts:220:10)
at Object.instantiateClass (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/resolver.ts:58:25)
at _setValueGetter (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/binding.ts:522:29)
at Binding._getValue (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/binding.ts:400:14)
at resolution_session_1.ResolutionSession.runWithBinding.s (/Users/xxxx/lb-4-todo-list/node_modules/@loopback/context/src/binding.ts:295:23)
at value_promise_1.tryWithFinally (/Users/xxxxx/lb-4-todo-list/node_modules/@loopback/context/src/resolution-session.ts:114:13)