update CHANGELOG

CHANGELOG.md

@@ -38,6 +38,7 @@ IMPROVEMENTS:
   - provisioners/salt: support specifying version to install [GH-5892]
   - provisioners/shell: add :name attribute to shell provisioner [GH-5607]
   - providers/docker: supports file downloads with the file provisioner [GH-5651]
+  - providers/docker: support named Dockerfile [GH-5480]
   - providers/hyperv: select a Hyper-V switch based on a `network_name` [GH-5207]
   - providers/hyperv: allow configuring VladID [GH-5539]
   - providers/virtualbox: regexp supported for bridge configuration [GH-5320]

website/docs/source/v2/docker/configuration.html.md

@@ -30,6 +30,9 @@ General settings:
     `docker run` when the container is started. This can be used to set
     parameters that aren't exposed via the Vagrantfile.
 
+  * `dockerfile` (string) - Name of the Dockerfile in the build directory.
+    This defaults to "Dockerfile"
+
   * `env` (hash) - Environmental variables to expose into the container.
 
   * `expose` (array of integers) - Ports to expose from the container