chore: add setup script

Added a setup script in scripts/ to configure Git to use the commit
message template and added a reference to it to README.md.

README.md

@@ -13,6 +13,10 @@ You can install it using pip:
 pip install jcloud-docsgen --index-url https://repo.jcloud-services.ddns.net/simple/ --extra-index-url https://pypi.org/simple/
 ```
 
+## Setup
+
+Please execute `scripts/setup.sh` when cloning the repository to configure Git.
+
 ## Reference
 
 API reference and generated documentation can be found in [docs/reference](docs/reference).