chore: update releases to 8 weeks in CONTRIBUTING (#30119)

* chore: update releases to 8 weeks in CONTRIBUTING

* chore: update support.md for four version support

Co-authored-by: Keeley Hammond <vertedinde@electronjs.org>
Co-authored-by: VerteDinde <khammond@slack-corp.com>

CONTRIBUTING.md

@@ -22,7 +22,7 @@ Issues are created [here](https://github.com/electron/electron/issues/new).
 
 ### Issue Closure
 
-Bug reports will be closed if the issue has been inactive and the latest affected version no longer receives support. At the moment, Electron maintains its three latest major versions, with a new major version being released every 12 weeks. (For more information on Electron's release cadence, see [this blog post](https://electronjs.org/blog/12-week-cadence).)
+Bug reports will be closed if the issue has been inactive and the latest affected version no longer receives support. At the moment, Electron maintains its three latest major versions, with a new major version being released every 8 weeks. (For more information on Electron's release cadence, see [this blog post](https://electronjs.org/blog/8-week-cadence).)
 
 _If an issue has been closed and you still feel it's relevant, feel free to ping a maintainer or add a comment!_
 

docs/tutorial/support.md

@@ -37,6 +37,13 @@ tools and resources.
 
 ## Supported Versions
 
+_**Note:** Beginning in September 2021 with Electron 15, the Electron team
+will temporarily support the latest **four** stable major versions. This
+extended support is intended to help Electron developers transition to
+the [new eight week release cadence](https://electronjs.org/blog/8-week-cadence), and will continue until May 2022, with
+the release of Electron 19. At that time, the Electron team will drop support
+back to the latest three stable major versions._
+
 The latest three *stable* major versions are supported by the Electron team.
 For example, if the latest release is 6.1.x, then the 5.0.x as well
 as the 4.2.x series are supported.  We only support the latest minor release