Update README.md, ci skip

the [official documentation](https://deepghs.github.io/imgutils/main/api_doc/validate/monochrome.html#module-imgutils.validate.monochrome)

.

### Image Rating

We can use `imgutils` to perform a rough and quick determination of the rating (`safe`, `r15`, or `r18`) of anime

images, as shown below.

![rating](https://github.com/deepghs/imgutils/blob/gh-pages/main/_images/rating.plot.py.svg)

```python

from imgutils.validate import anime_rating

print(anime_rating('rating/safe/1.jpg'))  # ('safe', 0.9999998807907104)

print(anime_rating('rating/safe/2.jpg'))  # ('safe', 0.9924363493919373)

print(anime_rating('rating/safe/3.jpg'))  # ('safe', 0.996969997882843)

print(anime_rating('rating/safe/4.jpg'))  # ('safe', 0.9966891407966614)

print(anime_rating('rating/r15/5.jpg'))  # ('r15', 0.9996721744537354)

print(anime_rating('rating/r15/6.jpg'))  # ('r15', 0.9998563528060913)

print(anime_rating('rating/r15/7.jpg'))  # ('r15', 0.9827859997749329)

print(anime_rating('rating/r15/8.jpg'))  # ('r15', 0.8339558839797974)

print(anime_rating('rating/r18/9.jpg'))  # ('r18', 0.9997004270553589)

print(anime_rating('rating/r18/10.jpg'))  # ('r18', 0.9997699856758118)

print(anime_rating('rating/r18/11.jpg'))  # ('r18', 0.9999485015869141)

print(anime_rating('rating/r18/12.jpg'))  # ('r18', 0.9994290471076965)

```

### Truncated Image Check

The following code can be used to detect incomplete image files (such as images interrupted during the download