This is a JSHint options file appropriate for Esri JS API based projects. It is the same file Esri uses internally for working on the JS API library.
It is an extended and slightly "nicer" version of the original JavaScript linting tool, jslint. JSHint is supported in all major web development IDEs and is widely used throughout the industry.
You can find out more information about the specific options here.
You can learn more about JSHint in general.
Most IDEs will traverse up your directory structure looking for a file named .jshintrc.
If you would like to use this file on a specific project or even part of a project, you should put it in that associated directory.
If you are interested in using this file for the majority of your projects, then you should put it somewhere higher up in your directory structure, such as your projects folder, for example.
Most IDEs will look up the directory structure, but never further down or in adjacent folders.
Please feel free to modify as appropriate for your own use.