Create ReScript.gitignore

[brettcannon]

Reasons for making this change: There is a lack of support for the ReScript programming language.

Links to documentation supporting these rule changes:

There was a discussion about what to include in the file. What is being proposed matches what a new project sets in its .gitignore file.

If this is a new template:

• Link to application or project’s homepage: https://rescript-lang.org/

[brettcannon]

I addressed the review comment (and apologies on the delay; new parent 😅).

[wirecat]

@brettcannon Thank you for the update! I can't throw stones about any delay here 😅. Thank you for contributing to the project!