Update CHANGELOG

@schneider, please take a look if everything BLE related looks right. The rendered CHANGELOG is here:

https://git.card10.badge.events.ccc.de/card10/firmware/-/blob/rahix/changelog/CHANGELOG.md

CHANGELOG.md

@@ -4,6 +4,56 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
+### For Users
+#### Added
+- Added the Bosch BSEC library for the BME680 sensor.  See the [``bme680``
+  module][bme680-docs] documentation for details.
+- Added a [BLE Environmental Sensing Service][ess-docs].
+- Added a [BLE HID Service][ble-hid-docs].
+- Added the ability to use the pulse-oximeter as a proximity sensor (makes it
+  usable as a button).  Additionally a demo-application was added which uses
+  this for a push-to-talk button.
+- Added a [blitting][blit-docs] function to the display module.  This finally
+  allows to efficiently draw pixels!
+- MicroPython BLE support!
+- A PNG library for pycardium: [`png`][png-docs]
+- Two more config options to tweak menu button behavior: `long_press_ms` and ``retrigger_ms``
+- Option to disable low battery checks via `card10.cfg`.  This is meant for
+  devices where the connection between the PMICs ADMUX and the CPU's ADC is broken
+  in some way, leading to the device always reporting a low battery condition.
+
+#### Changed
+- Updated the BME680 demo app with BSEC support.
+- Upgraded to MicroPython 1.14.
+- Open the USB mass-storage when no apps are found.
+- Improved the l0dables runtime; it now handles HardFaults and app-exits
+  properly.
+
+#### Fixed
+- Fixed lockup when trying to load an ELF l0dable while ELFs are disabled.
+- Fixed card10 not waking up from sleep when BLE is disabled (regression from 1.15 to 1.16).
+- Fixed card10 not working with the Harmonic Board disconnected (regression from
+  1.15 to 1.16).
+
+#### Removed
+- Removed the battery BLE service.
+
+### Internals
+#### Added
+- A work-queue API in Epicardium to schedule work that needs to be done
+  asynchronously.
+
+#### Changed
+- Upgraded to newer SDK version.
+- Cleaned up the BHI160 driver a bit.
+- Readjusted the flash layout, to give Epicardium more space.
+- Upgraded the documentation to use Sphinx 3.
+
+[bme680-docs]: https://firmware.card10.badge.events.ccc.de/pycardium/bme680.html
+[ess-docs]: https://firmware.card10.badge.events.ccc.de/bluetooth/ess.html
+[ble-hid-docs]: https://firmware.card10.badge.events.ccc.de/pycardium/ble_hid.html
+[blit-docs]: https://firmware.card10.badge.events.ccc.de/pycardium/display.html#display.Display.blit
+[png-docs]: https://firmware.card10.badge.events.ccc.de/pycardium/png.html
 
 
 ## [v1.16] - 2020-12-04 - [Pandemic Potato]