Update or remove link to Atmosphere IoT

[jaller94]

Atmosphere IoT has removed linked page.

webthingsio.github.io/framework/index.html

Lines 946 to 948 in ee6bf47

	<a href="https://developer.atmosphereiot.com/documents/guides/gettingstartedwebthings.html">
	<img alt="Atmosphere IoT logo" src="images/atmosphere_iot.svg" />
	Atmosphere IoT

Searching for WebThings in their documentation only yields the addition of support in the release log of v1.3.9.