Added a .gitignore template for RoR projects

[Tomax47]

Reasons for making this change: Couldn't find no Ruby on Rails gitignore template in the repo!

Examples of projects utilizing same/similar template:

1- https://github.com/maybe-finance/maybe 2- https://github.com/docusealco/docuseal 3- https://github.com/shakacode/react_on_rails

I also use this template in one of my own personal projects.

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