Closes #3: [Enhancement] Add README on the structure of the app and usages

Signed-off-by: Peter Zhu <zhujiaxi@amazon.com>

Author: peterzhuamazon

README.md

@@ -15,6 +15,39 @@ This repository hosts the source code of an automation app to handle the daily a
 
 The automation app utilizes the [Probot](https://probot.github.io/) framework and [Octokit](https://docs.github.com/en/rest/using-the-rest-api/libraries-for-the-rest-api?apiVersion=2022-11-28) library to perform user-defined operations on top of the resources within GitHub. See [configs](configs/operations/hello-world.yml) yaml for more information.
 
+## Usages
+
+### Service
+
+A **Service** is an instance of the app that manages and manipulates specific `Resources` while performing defined `Operations`.
+* **Resource**: Objects or entities the service will manage or modify, such as GitHub organizations, project, repositories, issues, etc.
+* **Operation**: A list of **Tasks** triggered by events with the resources.
+* **Task**: Executed sequentially within an **Operation** to perform action, such as create comments, update labels, add issue to project, etc.
+* **Call**: The callstack that contains the implementation of the aformentioned task action.
+
+### Create a Service
+
+To create a service, you need two configuration files:
+* **Resource configuration file**: Defines the resources that the service will manage or modify (`configs/resources/sample-resource.yml`).
+* **Operation configuration file**: Defines the operations (tasks) that the service will execute with the resources (`configs/resources/sample-operation.yml`).
+
+### Start the Service
+
+Once you have created the resource and operation configuration files, follow these steps to start the service:
+
+1. Set the `RESOURCE_CONFIG` environment variable to the path of the resource configuration YAML file.
+1. Set the `OPERATION_CONFIG` environment variable to the path of the operation configuration YAML file.
+1. Run the service using the following command:
+
+```bash
+RESOURCE_CONFIG=configs/resources/sample-resource.yml OPERATION_CONFIG=configs/operations/sample-operation.yml npm start
+```
+
+When you run the above command, the following takes place:
+1. The app starts a **Service** instance based on the specified configurations.
+1. Retrieves the **[GitHub Context](https://probot.github.io/api/latest/classes/context.Context.html)** (or any other defined context) for all the resources listed in the resource config file.
+1. Registers and listens for events, executes the **Tasks** defined in the operation config. These tasks will be executed sequentially when the corresponding events occur.
+
 ## Code of Conduct
 
 This project has adopted [the Open Source Code of Conduct](CODE_OF_CONDUCT.md).

src/app.ts

@@ -6,7 +6,13 @@ export default async (app: Probot) => {
   app.log.info('OpenSearch Automation App is starting now......');
 
   const srvObj = new Service('Hello World Service');
-  await srvObj.initService(app, 'configs/resources/peterzhu-organization.yml', 'configs/operations/hello-world.yml');
+  const resourceConfig: string = process.env.RESOURCE_CONFIG || '';
+  const processConfig: string = process.env.OPERATION_CONFIG || '';
+
+  if (resourceConfig === '' || processConfig === '') {
+    throw new Error(`Invalid config path: RESOURCE_CONFIG=${resourceConfig} or OPERATION_CONFIG=${processConfig}`);
+  }
+  await srvObj.initService(app, resourceConfig, processConfig);
 
   app.log.info('All objects initialized, start listening events......');
 };