Documentation: Edit Dynamic Default Values docs to cover multiple relation fields

content/docs/dynamic-default-values.md

@@ -35,4 +35,36 @@ clicking the following link: `/#/collections/posts/new?title=first&object.title=
 will open the editor for a new post with the `title` field populated with `first`, the nested `object.title` field
 with `second` and the markdown `body` field with `# content`.
 
+Here's an example using a multiple relation field. Given the configuration:
+
+```yaml
+collections:
+  - name: posts
+    label: Posts
+    folder: content/posts
+    create: true
+    fields:
+      - label: Title
+        name: title
+        widget: string
+      - label: Authors
+        name: authors
+        widget: relation
+        collection: "authors"
+        value_field: "name"
+        multiple: true
+  - name: authors
+    label: Authors
+    folder: content/authors
+    create: true
+    fields:
+      - label: Name
+        name: name
+        widget: string
+```
+
+clicking the following link: `/#/collections/posts/new?authors=first&authors=second`
+
+will open the editor for a new post with the `authors` field populated with any pre-existing authors whose names match `first` and `second`.
+
 **Note:** URL Encoding might be required for certain values (e.g. in the previous example the value for `body` is URL encoded).