docs(README): add "pre-commit install --hook-type commit-msg" command to pre-commit section

Lee-W · Lee-W · commit a3019c898d1f · 2020-07-04T19:04:34.000+08:00
diff --git a/docs/README.md b/docs/README.md
@@ -88,6 +88,12 @@ repos:
         stages: [commit-msg]
 ```
 
+After the configuration is added, you'll need to run
+
+```sh
+pre-commit install --hook-type commit-msg
+```
+
 Read more about the `check` command [here](https://commitizen-tools.github.io/commitizen/check/).
 
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