Document jreleaser/jreleaser#1049

docs/modules/reference/pages/packagers/docker.adoc

@@ -30,6 +30,9 @@ The following artifact extensions are supported by this packager:
 IMPORTANT: Building and publishing docker images requires the `docker` command and a running Docker deamon.
 JReleaser will not install these tools.
 
+NOTE: `docker.io` will be set as default registry (with "DEFAULT" as name) if no registries are configured. The chosen
+username will be set to match the Git username.
+
 include::partial$legend.adoc[]
 
 [tabs]
@@ -88,7 +91,6 @@ include::partial$packagers/yaml/tap.adoc[]
       foo: bar
 
     # A list of docker registries where images will be published.
-    # Image publication will be disabled if no registries are configured.
     # icon:dot-circle[]
     registries:
 
@@ -172,7 +174,6 @@ include::partial$packagers/toml/tap.adoc[]
   labels.foo = "bar"
 
   # A list of docker registries where images will be published.
-  # Image publication will be disabled if no registries are configured.
   # icon:dot-circle[]
   pass:[[[packagers.docker.registries]]]
     # The name of the registry. Must be unique.
@@ -263,7 +264,6 @@ include::partial$packagers/json/tap.adoc[]
       },
 
       // A list of docker registries where images will be published.
-      // Image publication will be disabled if no registries are configured.
       // icon:dot-circle[]
       "registries": [
 
@@ -374,7 +374,6 @@ include::partial$packagers/maven/tap.adoc[]
 
       <!--
         A list of docker registries where images will be published.
-        Image publication will be disabled if no registries are configured.
         icon:dot-circle[]
       -->
       <registries>
@@ -471,7 +470,6 @@ include::partial$packagers/gradle/tap.adoc[]
       label('foo', 'bar')
 
       // A list of docker registries where images will be published.
-      // Image publication will be disabled if no registries are configured.
       // icon:dot-circle[]
       registries {