[Docs] Add section about EEPROM on ARM (#5070)

* [Docs] Add section about EEPROM on ARM

* Add Preonic firmware

* Update docs/faq_build.md

add hyperlink

Co-Authored-By: yanfali <yanfali@gmail.com>

docs/faq_build.md

@@ -132,3 +132,11 @@ brew uninstall --force avr-gcc
 brew install avr-gcc@7
 brew link --force avr-gcc@7
 ```
+
+### I just flashed my keyboard and it does nothing/keypresses don't register - it's also ARM (rev6 planck, clueboard 60, hs60v2, etc...) (Feb 2019)
+Due to how EEPROM works on ARM based chips, saved settings may no longer be valid.  This affects the default layers, and *may*, under certain circumstances we are still figuring out, make the keyboard unusable.  Resetting the EEPROM will correct this.
+
+[Planck rev6 reset EEPROM](https://cdn.discordapp.com/attachments/473506116718952450/539284620861243409/planck_rev6_default.bin) can be used to force an eeprom reset. After flashing this image, flash your normal firmware again which should restore your keyboard to _normal_ working order.
+[Preonic rev3 reset EEPROM](https://cdn.discordapp.com/attachments/473506116718952450/537849497313738762/preonic_rev3_default.bin)
+
+If bootmagic is enabled in any form, you should be able to do this too (see [Bootmagic docs](feature_bootmagic.md) and keyboard info for specifics on how to do this).