Include minimum browser support requirements for developers in README

[wisniewski94]

I noticed in source code arrow functions next to regular functions, as well as vars and let/const. At first I thought it's written to support even old browsers but it doesn't make sense with ES6 features.

Code needs to be refactored/cleaned up according to clean-code-javascript but we need to decide what browser support this project provides.

I would recommend to drop IE support and there are multiple reasons to do so.

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[YogeshSharma01]

Hi, @wisniewski94 You working on it?

[Ayush-1127]

will you please explain the issue