tweak set_content_encoding docs

actix-files/src/named.rs

@@ -299,9 +299,11 @@ impl NamedFile {
         self
     }
 
-    /// Set content encoding for serving this file
+    /// Sets content encoding for this file.
     ///
-    /// Must be used with `actix_web::middleware::Compress` to take effect.
+    /// This prevents the `Compress` middleware from modifying the file contents and signals to
+    /// browsers/clients how to decode it. For example, if serving a compressed HTML file (e.g.,
+    /// `index.html.gz`) then use `.set_content_encoding(ContentEncoding::Gzip)`.
     #[inline]
     pub fn set_content_encoding(mut self, enc: ContentEncoding) -> Self {
         self.encoding = Some(enc);