doc: clarify that Gogland is for paid IntelliJ platform IDEs

Fixes #21213.

Change-Id: I7b8a84de92bbd1d3f78f8a9612f3af8cd092cb94
Reviewed-on: https://go-review.googlesource.com/53351Reviewed-by: Andrew Bonventre <andybons@golang.org>

doc/editors.html

@@ -23,7 +23,7 @@ editing, navigation, testing, and debugging experience.
 <li><a href="https://marketplace.visualstudio.com/items?itemName=lukehoban.Go">Visual Studio Code</a>:
 Go extension provides support for the Go programming language</li>
 <li><a href="https://www.jetbrains.com/go">Gogland</a>: Gogland is distributed either as a standalone IDE
-or as a plugin for the IntelliJ Platform IDEs</li>
+or as a plugin for the paid IntelliJ Platform IDEs</li>
 <li><a href="https://atom.io/packages/go-plus">Atom</a>: Go-Plus is an Atom package that provides enhanced Go support</li>
 </ul>