hardware/README.md: add Q3 Q4

[pd0wm]

First of all, thanks for open sourcing the design! Very excited to try it out.

Q3 and Q4 where missing from the table. This PR adds AO3422 as from the xls BOM.

The suggest sub part (PMV37ENEAR) is now also out of stock on digikey/farnell. Any suggestions for a different sub?

I also made a list with Farnell part numbers (https://docs.google.com/spreadsheets/d/1lR9KH1mVs3pNZHqpcGG9F5pi7PmbyUwxurxPG0W1xi4/edit?usp=sharing). Feel free to use that list for whatever you want.

[colinoflynn]

Great thanks! I'll add that link to the README if OK with you (or can commit to the repo?).

I opened issue #5 to track part subs. For some reason these logic-level MOSFETs in SOT-23 have had stock issues for past couple of years - I've run into this on our other products. The best sub I could recommend is just lowering the voltage, you don't actually need the high voltage I use. I'll add some notes to that issue/readme.

[colinoflynn]

@pd0wm I added a few notes to #5 about the MOSFET, hopefully helpful in finding one. Unfortunately it seems this game may need to be played a few times. If you're able to find something useful I'd just get it and not worry about looking for large stock numbers, from what I've seen this changes quickly anyway...

[pd0wm]

Great thanks! I'll add that link to the README if OK with you (or can commit to the repo?).

Adding a link is fine with me. But adding the contents to the repo allows other people to update it as parts go in and out if stock, so that might make more sense if you plan on actively maintaining this repo.