docs: Improve documentation on the --debug flag (#766)

Fixes  #764; clarifies the purpose of switching to the `listr-verbose-renderer` module.

README.md

@@ -86,7 +86,7 @@ Options:
 - **`--quiet`**: By default `lint-staged` will print progress status to console while running linters. Use this flag to supress all output, except for linter scripts.
 - **`--debug`**: Enabling the debug mode does the following:
   - `lint-staged` uses the [debug](https://github.com/visionmedia/debug) module internally to log information about staged files, commands being executed, location of binaries, etc. Debug logs, which are automatically enabled by passing the flag, can also be enabled by setting the environment variable `$DEBUG` to `lint-staged*`.
-  - Use the [`verbose` renderer](https://github.com/SamVerschueren/listr-verbose-renderer) for `listr`.
+  - Use the [`verbose` renderer](https://github.com/SamVerschueren/listr-verbose-renderer) for `listr`; this causes serial, uncoloured output to the terminal, instead of the default (beautified, dynamic) output.
 - **`--concurrent [number | (true/false)]`**: Controls the concurrency of tasks being run by lint-staged. **NOTE**: This does NOT affect the concurrency of subtasks (they will always be run sequentially). Possible values are:
   - `false`: Run all tasks serially
   - `true` (default) : _Infinite_ concurrency. Runs as many tasks in parallel as possible.