Created by: Lucretiel
Because the master branch is the authoritative source of documentation, it can be confusing for developers who have used npm install gulp (or joined a project using gulp 3) that the master branch is for a different major release. This PR adds a simple notification to the API docs, which are linked to from https://gulpjs.com/, that the standard version installed by npm install gulp.
It's worth noting that, while it might be obvious to people familiar with gulp's development, there's no indication that there's a mismatch between master and the current node release anywhere on https://gulpjs.com/, nor on master:docs/API.md, nor in any of the top google search results for "gulpjs documentation".