docs: Provide an example of multiple groups

Author: epage

src/snippet.rs

@@ -22,6 +22,13 @@ pub(crate) struct Id<'a> {
 /// A [diagnostic][crate::Renderer::render] is made of several `Group`s.
 /// `Group`s are used to [annotate][AnnotationKind::Primary] [`Snippet`]s
 /// with different [semantic reasons][Title].
+///
+/// # Example
+///
+/// ```rust
+#[doc = include_str!("../examples/highlight_message.rs")]
+/// ```
+#[doc = include_str!("../examples/highlight_message.svg")]
 #[derive(Clone, Debug)]
 pub struct Group<'a> {
     pub(crate) primary_level: Level<'a>,