Add about timeout and how to fix it (#111)

* Add about timeout and how to fix it

* Update README.md

Co-authored-by: Hannes Ljungberg <hannes@5monkeys.se>

README.md

@@ -280,6 +280,7 @@ Using that you can make rules like "If temperature drops below 21C and someone i
 ## Known problems
 Some hardware combinations are problematic and may cause weird troubles like sensor timeout after some time etc.
 * Asus BT-400 bluetooth dongle (at least in combination with older RPi 2B)
+* Raspbian Stretch is known to get recurring timeouts with certain RPi-models. Upgrade to Buster or newer and if not possible one can mitigate this by triggering a `hcitool lescan`. Automate this by adding the following to your crontab file: `0 * * * * sudo timeout -s INT 1s hcitool lescan`.
 
 ## Legal