Add power pin limits callout to Photon datasheet.

[harrisonhjones]

Added power pin limits to power section of Photon datasheet.

@moors7 mentioned that we could also add it to the FAQ. I looked through it and I don't see a good section in the FAQ to add it to. Thoughts?

[monkbroc]

I think the datasheet is sufficient.

[monkbroc]

I queued this up in #19 so we include this in the next datasheet revision.

[harrisonhjones]

@monkbroc Do you mean the datasheet as is is sufficient? or that you accept this PR?

[monkbroc]

I meant that adding the info to the datasheet only, not the faq also, is sufficient. The PR is good 👍

I did not merge it so we can bundle all the datasheet changes together.

[moors7]

Though it should suffice to put it in the datasheet, it definitely wouldn't hurt to put it in the FAQ as well, since it's not the first time that question (or a variation thereof) has come up. Perhaps a 'power section' is in order, highlighting the various 'specialties', current per pin, current for Vin/3.3V, tying Vbat to ... when not in use, etc.
Most/all the info is in the datasheets, but from the forum questions it's evident that those aren't always as easy to find. Just my 2 cents.

[technobly]

I also think it's good to keep all of the numbers in one place as much as possible, i.e. the datasheet. That way if we update those numbers we don't have to remember all of the other places where they were copied. The FAQ could point to the datasheets for limits.

[moors7]

Fair enough, it's a valid compromise. With that in mind, in this specific situation it seems unlikely those values will change (it's a hardware limitation?). With something like the LED patterns it makes more sense to keep those in one place, as opposed to the current three ;)

[technobly]

Just updating the datasheets, and after considering this entry, it seems redundant since we have a Technical Specification section already with Absolute Maximum Ratings:
https://docs.particle.io/datasheets/photon-datasheet/#absolute-maximum-ratings

I'll add a link to that section in the Power section.

Thanks for the PR!