Document default value

Author: LaurenzV

src/chunk.rs

@@ -9,6 +9,8 @@ pub struct Settings {
     /// If disabled, `pdf-writer` will serialize objects as compactly as
     /// possible, leading to better file sizes but making it harder to inspect
     /// the file manually.
+    /// 
+    /// _Default value_: `true`.
     pub pretty: bool,
 }