Documentation inconsistency

[DonGiulio]

I found in the docs an inconsistency in the versions required for the installation of Android for Mac.

the text mentions Look for and expand the Android 6.0 (Marshmallow) and Android SDK Platform 23 but the screenshot shows that Android 8.0 is used and different packages selected. and version 26 is checked.

similarly, below the text mentions: then make sure that 23.0.1 is selected. while the screenshot show 26.0.3 selected.

I'm installing this stuff for the first time, and this is very confusing, I'll try to use the newer versions, mentioned in the screenshots.

[hramos]

We've been bumping the Android SDK deps in recent weeks: facebook/react-native#19297

Docs have fallen out of sync, unfortunately. We'd appreciate a PR to bring them up to speed. You can look at the changelogs to understand the actual recommended versions.