New page for Solar Air Monitor Docs

[eugenethreat]

@amarischen for you

[hawc2]

@amarischen @eugenethreat I've transferred Amaris' pdf guide on building solar-powered IoT devices to the docs. I'm going to merge it but Amaris I'd welcome you to review it and help do edits. There's no rush to get it perfect, but once we get the new set of parts delivered, we'll hopefully be able to have a working prototype.

From what I've gleaned from our conversations and from looking through the guide and relevant documentation, these seem to be the main issues currently:

1. The box draws about double what it was sized for. The 21.6Wh/day budget covers only the PurpleAir. The temperature disconnect's relay draws about 20Wh/day on its own, and the buck converter loses another 12%, which puts the total around 36-45Wh/day.
2. The 10Ah battery has little or no margin at that load. It's about three days of backup at best, and the BMS cuts off before the battery is empty.
3. The 10W panel is too small for winter. In December it makes about 18Wh a day, less than the monitor alone uses. Voltaic recommends 20W for one monitor.

So we're buying a 20W panel, using the 20Ah battery. We could look into batteries with built-in weather charge protection, since that does burn energy. But these are estimates from spec sheets, so it may be off.