Add better error message for file save failure due to parent not existing (#7014)

Fixes #5229

helix-view/src/document.rs

@@ -808,7 +808,7 @@ impl Future<Output = Result<DocumentSavedEvent, anyhow::Error>> + 'static + Send
                     if force {
                         std::fs::DirBuilder::new().recursive(true).create(parent)?;
                     } else {
-                        bail!("can't save file, parent directory does not exist");
+                        bail!("can't save file, parent directory does not exist (use :w! to create it)");
                     }
                 }
             }