docs: document fetchFn

Author: ahmedriad1

docs/src/pages/_meta.json

@@ -1,10 +1,11 @@
 {
   "index": "Introduction",
+  "techniques": "Techniques",
   "chapters": "Chapters",
   "verses": "Verses",
   "search": "Search",
   "juzs": "Juzs",
   "audio": "Audio",
   "resources": "Resources",
   "utils": "Utilities"
-}
+}

docs/src/pages/techniques.mdx

@@ -0,0 +1,39 @@
+## Custom fetcher
+
+By default, all functions that interact with the [Quran.com API](https://quran.api-docs.io/v4) use the global `fetch` function.
+
+You can override this by passing a custom fetcher (as `fetchFn`) to the options object of any method.
+
+import { Callout } from 'nextra-theme-docs';
+
+<Callout>
+  Note that the `fetchFn` accepts a string url and must return a promise with
+  the JSON response.
+</Callout>
+
+### Examples
+
+#### Axios
+
+```ts
+import axios from 'axios';
+
+const chapters = await quran.v4.chapters.findAll({
+  fetchFn: (url) => axios.get(url).then((res) => res.data),
+});
+```
+
+---
+
+#### Node-fetch
+
+```ts
+import fetch from 'node-fetch';
+
+const chapters = await quran.v4.chapters.findAll({
+  fetchFn: async (url) => {
+    const response = await fetch(url);
+    return response.json();
+  },
+});
+```