Add FAQ (#1098)

docs/docs/running-bracket/configuration.md

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 # Configuration

docs/docs/running-bracket/faq.md

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+# FAQ
+
+## I ran Bracket with the default `docker-compose.yml` but I can't connect to the backend?
+
+This is likely because you are trying to access Bracket on a different address than
+`http://localhost:3000` in the browser. In that case, two things need to be changed:
+
+- Change `NEXT_PUBLIC_API_BASE_URL` to the address of the backend, e.g `https://api.example.org`.
+- You will also need to update `CORS_ORIGINS` to the address of the frontend, e.g.
+  `https://app.example.org`.
+
+Please consult [configuration docs](configuration.md) for more information.