Merge pull request #597 from gravyboat/gh-pages

Add after_success and branch examples (#1)

Author: plaindocs

user/docker.md

@@ -137,6 +137,20 @@ Within your `.travis.yml` prior to attempting a `docker push` or perhaps before
 docker login -e="$DOCKER_EMAIL" -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD"
 ```
 
+#### Branch Based Registry Pushes
+
+To push a particular branch of your repository to a remote registry,
+use the `after_success` section of your `.travis.yml`:
+
+```yaml
+
+after_success:
+  - if [ "$TRAVIS_BRANCH" == "master" ]; then
+    docker login -e="$DOCKER_EMAIL" -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD";
+    docker push USER/REPO;
+    fi
+```
+
 #### Private Registry Login
 
 When pushing to a private registry, be sure to specify the hostname in the