doc: add faq - how to start with pm2

docs/source/faq.md

@@ -11,3 +11,26 @@ If you have questions that is not contained below, please check [egg issues](htt
 
 Process management is very important. It defines the way we write code, meanwhile relates to deep runtime optimization. So we think it's better defined by framework itself.
 
+## How to start application with PM2?
+
+Although PM2 is not recommanded, you can use it anyway.
+
+Firstly, put a start file in the root directory of your project:
+
+```js
+// server.js
+const egg = require('egg');
+
+const workers = Number(process.argv[2] || require('os').cpus().length);
+egg.startCluster({
+  workers,
+  baseDir: __dirname,
+});
+```
+
+We can start application with PM2 like this:
+
+```bash
+pm2 start server.js
+```
+

docs/source/zh-cn/faq.md

@@ -11,6 +11,25 @@ title: 常见问题
 
 进程模型非常重要，会影响到开发模式，运行期间的深度优化等，我们认为可能由框架来控制比较合适。
 
+## 如何使用 PM2 启动应用？
 
+尽管我们不推荐使用 PM2 启动，但仍然是可以做到的。
 
+首先，在项目根目录定义启动文件：
 
+```js
+// server.js
+const egg = require('egg');
+
+const workers = Number(process.argv[2] || require('os').cpus().length);
+egg.startCluster({
+  workers,
+  baseDir: __dirname,
+});
+```
+
+这样，我们就可以通过 PM2 进行启动了：
+
+```bash
+pm2 start server.js
+```