Update documentations

docs/api-documents.md

@@ -1,4 +1,4 @@
-# API Documents for WGDashboard
+# 📖 API Document for WGDashboard
 
 **Version: v4.0**
 
@@ -6,3 +6,21 @@
 
 <hr>
 
+## 🔑 How to use API Key?
+
+### Create API Key
+
+1. To request an API Key, simply login to your WGDashboard, go to **Settings**, scroll to the very bottom. Click the **switch** on the right to enable API Key.
+2. Click the blur **Create** button, set an **expiry date** you want or **never expire**, then click **Done**.
+
+### Use API Key in `fetch()`
+
+```javascript
+fetch('http://server:10086', {
+    headers: {
+       'content-type': 'application/json',
+        'wg-dashboard-apikey': 'insert your api key here'
+    }
+})
+```
+To use API Key, simply insert `wg-dashboard-apikey` with the value of your API key into the `header` in your http request.