Updating readme and adding test_config_updates

In this issue, we will address minor issues in the README and enhance the tests to fulfill the requirements of the prepare-freva Makefile command.

Tasks:

• Fix the issues in the README.
• Implement test_config_updates.py in the \{\{cookiecutter.plugin_slug\}\}/src/tests/ directory as outlined in the Climate Change Profile (CCP) repository.
• Update the \{\{cookiecutter.plugin_slug\}\}/src/tests/conftest.py file to match the structure and functionality provided in the conftest.py file of CCP.
• Also move reuse section in README of plugins to another place. It could be located in this place