feat: use commit message template value as prefix

[MichaelCurrin]

resolves #63

Progress:

• [x] Read config value
• [x] Read file
• [ ] Functionality and tests to use a given prefix in a commit message
• [ ] Functionality and tests to tie the config file and commit message together. TBD how to mock the existence of config value
• [ ] Integration tests for reading config and file in the sample repo? Even if using mocks for file contents
• [ ] Documentation updates