docs: add example for custom registires (#161)

Author: xoxys

.dictionary

@@ -15,3 +15,4 @@ host:ip
 drone-docker-buildx
 multiarch
 buildx
+DockerHub

_docs/content/_index.md

@@ -50,6 +50,28 @@ steps:
 <!-- spellchecker-enable -->
 <!-- prettier-ignore-end -->
 
+### Examples
+
+**Push to other registries than DockerHub:**
+
+If the created image is to be pushed to registries other than the default DockerHub, it is necessary to set `registry` and `repo` as fully-qualified name.
+
+```YAML
+kind: pipeline
+name: default
+
+steps:
+  - name: docker
+    image: thegeeklab/drone-docker-buildx
+    privileged: true
+    settings:
+      registry: ghcr.io
+      username: octocat
+      password: secret-access-token
+      repo: ghcr.io/octocat/example
+      tags: latest
+```
+
 ## Build
 
 Build the binary with the following command:

_docs/data/data.yaml

@@ -191,7 +191,9 @@ properties:
     required: false
 
   - name: repo
-    description: Repository name for the image.
+    description: |
+      Repository name for the image. If the image is to be pushed to registries other than the default DockerHub,
+      it is necessary to set `repo` as fully-qualified name.
     type: string
     required: false