docs(project-definition): container registry settings

Author: saitho

Documentation/introduction/project-definition.md

@@ -41,6 +41,14 @@ domains:
           username: user
           password: pass
 container:
+  registries:
+    # Authenticate with Docker Hub for private images
+    - username: mydockerhubuser
+      password: mydockerhubpassword
+    # Authenticate with custom Docker registry
+    - username: myuser
+      password: mypassword
+      url: https://myregistry.com
   services:
     - name: app # service name
       image: nginxdemos/hello:latest # Docker image name
@@ -137,6 +145,22 @@ domains:
 Right now, removing a single entry from the list and redeploying the project will NOT remove the user settings from the authentication file.
 {% endhint %}
 
+### container.registries
+
+The following configuration options are available inside a registry definition:
+
+#### username
+
+Username for authentication with the container registry. Required.
+
+#### password
+
+Password for authentication with the container registry. Required.
+
+#### url
+
+URL of container registry. If none given, it will try to authenticate with Docker Hub.
+
 ### container.services
 
 The following configuration options are available inside a service definition: