Move Docker documentation to the local installation section

Having it under the production installation section was confusing, since
it contains instructions for local development.

docs/en/SUMMARY.md

@@ -15,6 +15,7 @@
     * [macOS](installation/macos.md)
     * [Windows](installation/windows.md)
     * [Vagrant](installation/vagrant.md)
+    * [Docker](installation/docker.md)
   * [Production and Staging servers](installation/servers.md)
     * [Installer](installation/installer.md)
     * [Create a deploy user](installation/create_deploy_user.md)
@@ -22,7 +23,6 @@
     * [Manual installation (not recommended)](installation/manual_installation_production.md)
     * [Digital Ocean](installation/digital_ocean.md)
     * [Heroku](installation/deploying-on-heroku.md)
-    * [Docker](installation/docker.md)
     * [Mail Server Configuration](installation/mail_server_configuration.md)
   * [Basic configuration](installation/basic_configuration.md)
   * [User documentation and guides](installation/documentation_and_guides.md)

docs/es/SUMMARY.md

@@ -15,6 +15,7 @@
     * [macOS](installation/macos.md)
     * [Windows](installation/windows.md)
     * [Vagrant](installation/vagrant.md)
+    * [Docker](installation/docker.md)
   * [Servidores de producción y pruebas](installation/servers.md)
     * [Instalador](installation/installer.md)
     * [Crear usuario](installation/create_deploy_user.md)
@@ -22,7 +23,6 @@
     * [Instalación manual (no recomendada)](installation/manual_installation_production.md)
     * [Digital Ocean](installation/digital_ocean.md)
     * [Heroku](installation/deploying-on-heroku.md)
-    * [Docker](installation/docker.md)
     * [Configuración del servidor de correo](installation/mail_server_configuration.md)
   * [Configuración básica](installation/basic_configuration.md)
   * [Documentación y guías de usuario](installation/documentation_and_guides.md)