better description

book/src/configuration.md

@@ -108,7 +108,7 @@ The following statusline elements can be configured:
 | `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) |
-| `read-only-indicator` | The indicator to show whether a file is read only |
+| `read-only-indicator` | An indicator that shows `[readonly]` when a file cannot be written |
 | `total-line-numbers` | The total line numbers of the opened file |
 | `file-type` | The type of the opened file |
 | `diagnostics` | The number of warnings and/or errors |