docs: added docs about how to use bknd.config.ts

docs/integration/react-router.mdx

@@ -22,21 +22,44 @@ To get started with React Router and bknd you can either install the package man
    </Tab>
 </Tabs>
 
+## Configuration
+Now create a `bknd.config.ts` file in the root of your project. If you created the project using the CLI starter, this file is already created for you.
+
+```typescript bknd.config.ts
+import type { ReactRouterBkndConfig } from "bknd/adapter/react-router";
+
+export default {
+   connection: {
+      url: "file:data.db"
+   }, 
+} satisfies ReactRouterBkndConfig;
+```
+
+See [bknd.config.ts](/extending/config) for more information on how to configure bknd. The `ReactRouterBkndConfig` type extends the `BkndConfig` type with the following additional properties:
+
+```typescript
+type ReactRouterEnv = NodeJS.ProcessEnv;
+type ReactRouterFunctionArgs = {
+   request: Request;
+};
+export type ReactRouterBkndConfig<Env = ReactRouterEnv> = FrameworkBkndConfig<Env>;
+```
+
 
 ## Serve the API
-Create a helper file to instantiate the bknd instance and retrieve the API:
+Create a helper file to instantiate the bknd instance and retrieve the API, importing the configurationfrom the `bknd.config.ts` file:
 
 ```ts app/bknd.ts
 import { type ReactRouterBkndConfig, getApp as getBkndApp } from "bknd/adapter/react-router";
+import config from "../bknd.config";
 
-const config = {
-   connection: {
-      url: "file:data.db"
-   }
-} as const satisfies ReactRouterBkndConfig;
+export { config };
 
-export async function getApp(args?: { request: Request }) {
-   return await getBkndApp(config, args);
+// you may adjust this function depending on your runtime environment.
+// e.g. when deploying to cloudflare workers, you'd want the FunctionArgs to be passed in
+// to resolve environment variables
+export async function getApp() {
+   return await getBkndApp(config, process.env as any);
 }
 
 export async function getApi(
@@ -60,7 +83,7 @@ Create a new api splat route file at `app/routes/api.$.ts`:
 import { getApp } from "~/bknd";
 
 const handler = async (args: { request: Request }) => {
-   const app = await getApp(args);
+   const app = await getApp();
    return app.fetch(args.request);
 };