update readme

Author: fatalxiao

README.md

@@ -1 +1,42 @@
-# http-proxy-middleware-body
+# http-proxy-middleware-body
+
+```javascript
+
+// ...
+
+const express = require('express'),
+    {createProxyMiddleware} = require('http-proxy-middleware'),
+
+    app = express();
+
+app.use(createProxyMiddleware(SOME_CONTEXT, {
+
+    // other configs...
+
+    onProxyRes: (proxyRes, req, res) => getBody(res, proxyRes, rawBody => {
+
+        if (!rawBody) {
+            return;
+        }
+
+        try {
+
+            // if it's a json body
+            const body = JSON.parse(rawBody);
+
+            // token expired
+            if (body.code === TOKEN_EXPIRED_CODE) {
+                // remove token...
+            }
+
+        } catch (e) {
+            // do something...
+        }
+
+    })
+
+}));
+
+// ...
+
+```