chore: stub out basic READMEs for all packages

packages/db-postgres/README.md

@@ -0,0 +1,28 @@
+# Payload Postgres Adapter
+
+Official Postgres adapter for [Payload](https://payloadcms.com).
+
+- [Main Repository](https://github.com/payloadcms/payload)
+- [Payload Docs](https://payloadcms.com/docs)
+
+## Installation
+
+```bash
+npm install @payloadcms/db-postgres
+```
+
+## Usage
+
+```ts
+import { buildConfig } from 'payload/config'
+import { postgresAdapter } from '@payloadcms/db-postgres'
+
+export default buildConfig({
+  db: postgresAdapter({}),
+  // ...rest of config
+})
+
+```
+
+More detailed usage can be found in the [Payload Docs](https://payloadcms.com/docs/configuration/overview).
+