quick doc on local development with multiple compose files

Author: jordanstephens

docs/concepts/local-development.md

@@ -0,0 +1,52 @@
+---
+title: Local Development
+description:
+sidebar-position: 800
+---
+
+# Local Development
+
+While Defang encourages using a single compose file, there are times when it is more convenient to use different files for different environments. For example, if some services should be configured differently locally: maybe you want to mount your working directory as a volume for live-reloading, or you want to build a different container image for local development. Another reason may be that you have some local services, like an auth mock or a local webhook listener that you don't want to deploy to the cloud.
+
+## `compose.local.yaml`
+
+In these cases, Defang recommends creating a file like `compose.local.yaml` which extends service definitions from your primary `compose.yaml` file.
+
+For example,
+
+```yaml
+# compose.yaml
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+```
+
+```yaml
+# compose.local.yaml
+services:
+  app:
+    extends:
+      file: compose.yaml
+      service: app
+    build:
+      context: .
+      dockerfile: local.Dockerfile
+    volumes:
+      - .:/web
+  local_service:
+    image: myservice:latest
+ ```
+
+This configuration can then be launched locally with
+
+```
+docker compose -f compose.local.yaml
+```
+
+And the primary compose file can be deployed to the cloud with
+
+```
+defang compose up
+```

docs/tutorials/deploy-to-gcp.mdx

@@ -13,7 +13,8 @@ This tutorial will show you how to deploy your services to your own GCP project
 * [A `compose.yaml` file in your project](https://docs.docker.com/compose/gettingstarted/)
 * [A Defang Account](/docs/concepts/authentication)
 * [The Defang CLI](/docs/getting-started#install-the-defang-cli)
-* [GCP Account Credentials](https://cloud.google.com/docs/authentication)
+* [gcloud CL](https://cloud.google.com/sdk/docs/install)
+* [GCP Account Credentials](https://cloud.google.com/docs/authentication/set-up-adc-local-dev-environment)
 
 ## Step 1 - Navigate to your project directory
 Head to the folder where your project is located.