docs(readme): add config file instructions

Author: bartholomej

README.md

@@ -20,7 +20,30 @@ npm install svelte-sitemap --save-dev
 
 ## Usage
 
-> Use this library as a `postbuild` hook in your `package.json` file.
+### Config file method (recommended)
+
+Create config file `svelte-sitemap.cjs` in the root of your project:
+
+`svelte-sitemap.cjs`
+
+```js
+module.exports = {
+  domain: 'https://www.example.com'
+  // ...more options
+};
+```
+
+Add `svelte-sitemap` as your postbuild script in `package.json` file:
+
+`package.json`
+
+```json
+{
+  "postbuild": "npx svelte-sitemap"
+}
+```
+
+### Alternative 1: CLI method
 
 File: `package.json`
 
@@ -35,7 +58,7 @@ File: `package.json`
 
 It scans your routes in `build/` folder and generates `build/sitemap.xml` file.
 
-### Alternative usage: TypeScript or JavaScript method
+### Alternative 2: TypeScript or JavaScript method
 
 > Sometimes it can be useful to call the script directly from JavaScript or TypeScript. Of course there is also this option, but in most cases you will need the [CLI method](#cli-method-recommended) as a postbuild hook.
 
@@ -49,6 +72,30 @@ createSitemap({ domain: 'https://example.com', debug: true });
 
 And now you can run your script like this: `node my-script.js`
 
+## Example
+
+Use this library as a `postbuild` hook in your `package.json` with config file `svelte-sitemap.cjs` in your project root.
+
+File: `package.json`
+
+```json
+{
+  "name": "my-project",
+  "scripts": {
+    "postbuild": "npx svelte-sitemap"
+  }
+}
+```
+
+File: `svelte-sitemap.cjs`
+
+```typescript
+module.exports = {
+  domain: 'https://www.example.com',
+  trailingSlashes: true
+};
+```
+
 ## ⚙️ Options
 
 | Option                     | Description                                                                                                                     | Default | Example                                |
@@ -136,6 +183,7 @@ yarn demo
 - svelte-sitemap is workaround for [this official SvelteKit issue](https://github.com/sveltejs/kit/issues/1142)
 - Brand new version is inspired by [Richard's article](https://r-bt.com/learning/sveltekit-sitemap/)
 - Thanks to [@auderer](https://github.com/auderer) because [his issue](https://github.com/bartholomej/svelte-sitemap/issues/1) changed the direction of this library
+- Config files inspired by [next-sitemap](https://github.com/iamvishnusankar/next-sitemap)
 
 ## 📝 License
 

src/vars.ts

@@ -5,10 +5,3 @@ export const DOMAIN = 'https://example.com';
 export const OUT_DIR = 'build';
 
 export const CONFIG_FILE = 'svelte-sitemap.cjs';
-
-// export const OPTIONS: Options = {
-//   domain: DOMAIN,
-//   resetTime: false,
-//   debug: false,
-//   changeFreq: 'weekly'
-// };