docs: More accuratly describe AnnotationKind variants

Author: Muscraft

src/snippet.rs

@@ -262,10 +262,13 @@ impl<'a> Annotation<'a> {
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[non_exhaustive]
 pub enum AnnotationKind {
-    /// Color to the [`Level`] the first [`Title`] in [`Group`]. If no [`Title`]
-    /// is present, it will default to `error`.
+    /// An [`Annotation`] which will use the "primary" underline character ('^'
+    /// for [`OutputTheme::Ascii`], and '━' for [`OutputTheme::Unicode`]) and
+    /// be colored according to the primary [`Level`] of the [`Group`].
     Primary,
-    /// "secondary"; fixed color
+    /// An [`Annotation`] which will use the "secondary" underline character (
+    /// '-' for [`OutputTheme::Ascii`], and '─' for [`OutputTheme::Unicode`])
+    /// and be colored according to [`Renderer::context`].
     Context,
 }