docs(compose): Inlude example for build secrets on the use-secrets doc (docker#20403)

* docs: Inlude example for build secrets

* Apply suggestions from code review

---------

Co-authored-by: Allie Sadler <102604716+aevesdocker@users.noreply.github.com>

Author: cefeboru

content/compose/use-secrets.md

@@ -84,7 +84,25 @@ In the advanced example above:
 >
 > The `_FILE` environment variables demonstrated here are a convention used by some images, including Docker Official Images like [mysql](https://hub.docker.com/_/mysql) and [postgres](https://hub.docker.com/_/postgres).
 
+### Build secrets
+
+In the following example, the `npm_token` secret is made available at build time. It's value is taken from the `NPM_TOKEN` environment variable.
+
+```yaml
+services:
+  myapp:
+    build:
+      secrets:
+        - npm_token
+      context: .
+
+secrets:
+  npm_token:
+    environment: NPM_TOKEN
+```
+
 ## Resources
 
 - [Secrets top-level element](compose-file/09-secrets.md)
 - [Secrets attribute for services top-level element](compose-file/05-services.md#secrets)
+- [Build secrets](https://docs.docker.com/build/building/secrets/)