Update firmware documentation to clarify update methods and warn abou… #647

Job	Run time
Prepare release data	4s
Build Docs / build-docs	24s
Build Nuki Bridge Firmware (Home Assistant, stable)	0s
Build Stock Firmware (Home Assistant, stable)	0s
Build Stock Firmware (Home Assistant, dev) / Prepare	3s
Build Nuki Bridge Firmware (Home Assistant, dev) / Prepare	1s
Build Nuki Bridge Firmware (Home Assistant, dev) / Build firmware/ha-doorman-nuki-bridge.dev.yaml	4m 26s
Build Stock Firmware (Home Assistant, dev) / Build firmware/ha-doorman-stock.dev.yaml	4m 46s
Create asset bundle (stable)	0s
Deploy to Github Pages (stable)	0s
Create asset bundle (dev) / Create asset bundle	10s
Deploy to surge.sh (dev)	22s
	10m 16s

Provide feedback