top page README.md is subject to staleness and rot by referencing a particular remote Arduino IDE level

Presently README.md states:

>   Install Arduino 1.8.2 from the Arduino website.

Checking the referenced site, it is actually now at:  1.8.3

Unless there is an articulated reason to 'freeze' at an older level, this statement might perhaps state:

>   Install the current upstream Arduino IDE at the 1.8 level or later.  The current version is (link)
