move postgres to a separate package

packages/postgres/README.md

@@ -0,0 +1,50 @@
+# Postgres adapter for `bknd` (experimental)
+This packages adds an adapter to use a Postgres database with `bknd`. It is based on `pg` and the driver included in `kysely`.
+
+## Installation
+Install the adapter with:
+```bash
+npm install @bknd/postgres
+```
+
+## Usage
+Create a connection:
+
+```ts
+import { PostgresConnection } from "@bknd/postgres";
+
+const connection = new PostgresConnection({
+   host: "localhost",
+   port: 5432,
+   user: "postgres",
+   password: "postgres",
+   database: "bknd",
+});
+```
+
+Use the connection depending on which framework or runtime you are using. E.g., when using `createApp`, you can use the connection as follows:
+
+```ts
+import { createApp } from "bknd";
+import { PostgresConnection } from "@bknd/postgres";
+
+const connection = new PostgresConnection();
+const app = createApp({ connection });
+```
+
+Or if you're using it with a framework, say Next.js, you can add the connection object to where you're initializating the app:
+
+```ts
+// e.g. in src/app/api/[[...bknd]]/route.ts
+import { serve } from "bknd/adapter/nextjs";
+import { PostgresConnection } from "@bknd/postgres";
+
+const connection = new PostgresConnection();
+const handler = serve({
+   connection
+})
+
+// ...
+```
+
+For more information about how to integrate Next.js in general, check out the [Next.js documentation](https://docs.bknd.io/integration/nextjs).