docs(README.md): update poetry dev dependency usage

Aleksandar Ivanovski · Lee-W · commit 5c335f5abd19 · 2022-11-17T17:07:31.000+08:00
Since Poetry 1.2.0 dependency groups are introduced, and `--dev` becomes deprecated, and instead `--with dev` has to be provided.
diff --git a/docs/README.md b/docs/README.md
@@ -59,7 +59,7 @@ pip install -U commitizen
 ```
 
 ```bash
-poetry add commitizen --dev
+poetry add commitizen --group dev
 ```
 
 ### macOS
