docs: run locally (#34)

README.md

@@ -15,3 +15,40 @@ which will be released soon!
 
 The app itself you can see live at
 **[kratos-reference-ui-react-nextjs.vercel.app](https://kratos-reference-ui-react-nextjs.vercel.app)**.
+
+<br />
+
+## Usage
+
+<br />
+
+**Environment**
+
+This application can be configured with the following environment variables
+_(refer to the
+[NextJS documentation](https://nextjs.org/docs/basic-features/environment-variables)
+to learn how to configure the application)_:
+
+- `ORY_SDK_URL` _(required)_<br />The URL where ORY Kratos's Public API is
+  located. If this app and ORY Kratos are running in the same private network,
+  this should be the private network address _(e.g.
+  `kratos-public.svc.cluster.local`)_.
+
+Example `.env.local`:
+
+```
+ORY_SDK_URL=http://localhost:4433/
+```
+
+<br />
+
+**Running Locally**
+
+The [quickstart documentation](https://www.ory.sh/kratos/docs/quickstart) guides
+developers to use port `4455` for the self-service UI. By default, NextJS uses
+port `3000`. Use the `-p` or `--port` option of the `next dev` / `next start`
+commands to set the port number:
+
+```sh
+npm run dev -- -p 4455
+```