[Doc] Tidy up compatible MCUs docs (#7295)

* Tidy up compatible MCUs docs

* ARM chips should have USB

* 32KB soft lower limit applies to ARM as well

* NXP is the manufacturer name, not Kinetis

* Units

2 files changed, 30 insertions, 18 deletions

diff --git a/docs/_summary.md b/docs/_summary.md
index dc6e88f958..808a8de4a0 100644
--- a/docs/_summary.md
+++ b/docs/_summary.md
@@ -33,6 +33,7 @@
   * [Keymap Overview](keymap.md)
 
 * [Hardware](hardware.md)
+  * [Compatible Microcontrollers](compatible_microcontrollers.md)
   * [AVR Processors](hardware_avr.md)
   * [Drivers](hardware_drivers.md)
 
diff --git a/docs/compatible_microcontrollers.md b/docs/compatible_microcontrollers.md
index 6e3f8372c9..85dd440d37 100644
--- a/docs/compatible_microcontrollers.md
+++ b/docs/compatible_microcontrollers.md
@@ -1,25 +1,36 @@
-# Atmel AVR
+# Compatible Microcontrollers
 
-QMK should run on any Atmel AVR processor with enough Flash. It has been tested on the following:
+QMK runs on any USB-capable AVR or ARM microcontroller with enough flash space - generally 32kB or more, though it will *just* squeeze into 16kB with most features disabled.
 
-* ATmega32U4 ([PJRC Teensy 2.0](http://www.pjrc.com/teensy/))
-* AT90USB1286 ([PJRC Teensy++ 2.0](http://www.pjrc.com/teensy/))
-* AT90USB1287 ([Atmel USBKEY](http://www.atmel.com/tools/AT90USBKEY.aspx))
-* ATmega168P with using [V-USB](http://www.obdev.at/products/vusb/index.html)
-* ATmega328P with using [V-USB](http://www.obdev.at/products/vusb/index.html)
-* ATmega32U2
-* AT90USB1286, 646, 647 should work
-* AT90USB162 testing...
+## Atmel AVR
 
-NOTE: To enable full features of firmware you'll need 32KB flash size.
+The following use [LUFA](https://www.fourwalledcubicle.com/LUFA.php) as the USB stack:
 
-Please add any tested microcontrollers to this list.
+* [ATmega16U2](https://www.microchip.com/wwwproducts/en/ATmega16U2) / [ATmega32U2](https://www.microchip.com/wwwproducts/en/ATmega32U2)
+* [ATmega16U4](https://www.microchip.com/wwwproducts/en/ATmega16U4) / [ATmega32U4](https://www.microchip.com/wwwproducts/en/ATmega32U4)
+* [AT90USB64](https://www.microchip.com/wwwproducts/en/AT90USB646) / [AT90USB128](https://www.microchip.com/wwwproducts/en/AT90USB1286)
 
-# ARM
+Certain MCUs which do not have native USB will use [V-USB](https://www.obdev.at/products/vusb/index.html) instead:
 
-You can also use any ARM processor that [ChibiOS](http://www.chibios.org) supports. The following processors have been tested:
+* [ATmega32A](https://www.microchip.com/wwwproducts/en/ATmega32A)
+* [ATmega328P](https://www.microchip.com/wwwproducts/en/ATmega328P)
 
-* [Kinetis MKL26Z64](http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/kinetis-cortex-m-mcus/l-series-ultra-low-power-m0-plus/kinetis-kl2x-48-mhz-usb-ultra-low-power-microcontrollers-mcus-based-on-arm-cortex-m0-plus-core:KL2x)
-* [Kinetis MK20DX128](http://www.nxp.com/assets/documents/data/en/data-sheets/K20P64M50SF0.pdf)
-* [Kinetis MK20DX128](http://www.nxp.com/assets/documents/data/en/data-sheets/K20P64M50SF0.pdf)
-* [Kinetis MK20DX256](http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/kinetis-cortex-m-mcus/k-series-performance-m4/k2x-usb/kinetis-k20-72-mhz-full-speed-usb-mixed-signal-integration-microcontrollers-mcus-based-on-arm-cortex-m4-core:K20_72)
+## ARM
+
+You can also use any ARM chip with USB that [ChibiOS](http://www.chibios.org) supports. Most have plenty of flash. Known to work are:
+
+### STMicroelectronics (STM32)
+
+ * [STM32F0x2](https://www.st.com/en/microcontrollers-microprocessors/stm32f0x2.html)
+ * [STM32F103](https://www.st.com/en/microcontrollers-microprocessors/stm32f103.html)
+ * [STM32F303](https://www.st.com/en/microcontrollers-microprocessors/stm32f303.html)
+
+### NXP (Kinetis)
+
+ * [MKL26Z64](https://www.nxp.com/products/processors-and-microcontrollers/arm-microcontrollers/general-purpose-mcus/kl-series-cortex-m0-plus/kinetis-kl2x-72-96-mhz-usb-ultra-low-power-microcontrollers-mcus-based-on-arm-cortex-m0-plus-core:KL2x)
+ * [MK20DX128](https://www.nxp.com/products/processors-and-microcontrollers/arm-microcontrollers/general-purpose-mcus/k-series-cortex-m4/k2x-usb/kinetis-k20-50-mhz-full-speed-usb-mixed-signal-integration-microcontrollers-based-on-arm-cortex-m4-core:K20_50)
+ * [MK20DX256](https://www.nxp.com/products/processors-and-microcontrollers/arm-microcontrollers/general-purpose-mcus/k-series-cortex-m4/k2x-usb/kinetis-k20-72-mhz-full-speed-usb-mixed-signal-integration-microcontrollers-mcus-based-on-arm-cortex-m4-core:K20_72)
+
+## Atmel ATSAM
+
+There is limited support for one of Atmel's ATSAM microcontrollers, that being the [ATSAMD51J18A](https://www.microchip.com/wwwproducts/en/ATSAMD51J18A) used by the [Massdrop keyboards](https://github.com/qmk/qmk_firmware/tree/master/keyboards/massdrop).