Changes to lower barrier of entry for new contributors

[zardini123]

This PR provides some changes to lower barrier of entry for new contributors. I found issues running tests, and the project's .gitignore did not follow practices of using virtual environments, which made contributing and testing my changes more time consuming. These changes are a first step to help future contributors ease into the codebase more.

• Adding CONTRIBUTING.md provides a developer-intended readme, which currently only includes documentation of getting a virtual environment setup and running KiUtil's tests. Encouraging developers to use virtual environments provides separation of project-specific vs global pip packages.
  • Guidelines can be added in the future here to set standards of contributing to this project (if necessary).
• The .gitignore additions of virtual environment folders reflects GitHub's community Python gitignore (here).
• I found when running test.py that the folder of kiutils under src/ could not be found, which is a issue multiple people have also had with Python's unittest module in a directory structure similar to KiUtils. My fix utilizes the StackExchange answer here to inject the kiutils source folder into PATH so all kiutil module references in test.py are found. Therefore, test.py can be ran without any specialized environment setup.

[mvnmgrx]

Thanks for those improvements! I agree, it is better to set the path to the sources directly in test.py instead of relying on the developer to set the environment up correctly. I will update the documentation accordingly.