Update TODO.md

TODO.md

@@ -3,4 +3,4 @@
 Additional implementation details to complement the specification:
 
 * circalog add a mode to track phone usage and auto input events, this way it can make an actogram out of smartphone use and infer indirectly sleep. Can be enabled for an event type, eg, Wakefulness. Smartphone usage is likely a very good proxy estimator of the wakefulness period since we use smartphones so much all the time!
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+* Add vibration feedback when tapping widgets to track or untrack sleep https://www.youtube.com/watch?v=rAVV4kAYlI8