Adds a gitignore file to the repo

[john-a-joyce]

Adds a gitignore so files in the repo can be ignored on the commit. Required because IDEs will add to repo but you want to ignore.

Thank you for contributing to this repo. Please use the following template to describe this Pull Request.

Summary of Problems addressed Need a gitignore file

Found In: path/to/file (if eligible) Top of tree

List of relevant Issues being fixed

Summary of Proposed Solution Add file

[tiswanso]

lgtm

[subodh-dharma]

@john-a-joyce Merged!