PPG analysis beyond HR at rest

I think it would be better to make this app work like the accellog app - where the data is stored in Flash and then downloaded later

There were discussions about this and I think @halemmerich had some troubles getting the relatively big file off the watch afterwards which is why he went direct.

Honestly, for the few HRM traces we need to get started, I think it's probably not the end of the world to have a phone in your pocket. It's not perfect I know, but it's not a reason not to use an app that does exactly what we need right now.

But yes, screen & readme could be added and I'm sure PRs for those would be appreciated - but again, I think there are probably only a handful of people that are going to actually do this with an external HRM, and for them a simple forum post with a few steps would work just fine