Update configuration docs

- Document the `file-modification-indicator` status line element
- Add a TODO to make it customizable

book/src/configuration.md

@@ -98,6 +98,7 @@ The following statusline elements can be configured:
 | `spinner` | A progress spinner indicating LSP activity |
 | `file-name` | The path/name of the opened file |
 | `file-base-name` | The basename of the opened file |
+| `file-modification-indicator` | The indicator to show whether the file is modified (a `[+]` appears when there are unsaved changes) |
 | `file-encoding` | The encoding of the opened file if it differs from UTF-8 |
 | `file-line-ending` | The file line endings (CRLF or LF) |
 | `total-line-numbers` | The total line numbers of the opened file |

helix-term/src/ui/statusline.rs

@@ -426,6 +426,7 @@ where
     write(context, title, None);
 }
 
+// TODO: Make this customizable (will entail an update in the `editor.statusline` section of `book/src/configuration.md`).
 fn render_file_modification_indicator<F>(context: &mut RenderContext, write: F)
 where
     F: Fn(&mut RenderContext, String, Option<Style>) + Copy,