Changelog 2021q4 (#15325)

* Changelog.

* Remove the asymmetric encoder PR from listing due to revert.

* More docs

* More docs

* More docs

* Links to changelog, updated schedule, slotted in 2 weeks of testing at the end so that there's no ambiguity with PR merge dates.

* Clarify keyboard moves.

* Fix dates

* Sidebar

* Fixup dates.

* Fixup dates.

* Wording.

docs/pr_checklist.md

@@ -118,6 +118,10 @@ Also, specific to ChibiOS:
 ## Core PRs
 
 - must now target `develop` branch, which will subsequently be merged back to `master` on the breaking changes timeline
+- any support for new hardware now requires a corresponding test board under `keyboards/handwired/onekey`
+    - for new MCUs, a new "child" keyboard should be added that targets your newly-added MCU, so that builds can be verified
+    - for new hardware support such as display panels, core-side matrix implementations, or other peripherals, an associated keymap should be provided
+    - if an existing keymap exists that can leverage this functionality this may not be required (e.g. a new RGB driver chip, supported by the `rgb` keymap) -- consult with the QMK Collaborators on Discord to determine if there is sufficient overlap already
 - other requirements are at the discretion of QMK collaborators
     - core is a lot more subjective given the breadth of posted changes