Mention supported browsers in documentation

## Description

Users of this library may need to support different browsers and, probably, their old enough versions. In order to understand, if this library suits their needs and supports those browsers and their versions too, it would be useful to define the supported browsers in the documentation explicitly.

## Describe the solution you'd like

Add to the documentation and to the `README.md` (optional) the following:

* List of supported browsers and their versions, like
* Chrome >= 10
* Firefox >= 11
* etc.
**and/or**
* Browserslist config, like "defaults and supports es6-module", so that users can check the supported browsers and their versions manually here: https://browsersl.ist/