add Amazon pins

If you're already buying the board from mouser it makes sense to get the pins from them, but if for people in the US who need long pins this is an Amazon prime option.

For example, I didn't buy pins because I already had some, but they were regular length which was too short. These Amazon pins worked well enough.

docs/shopping.md

@@ -12,7 +12,7 @@ Main part of the device is the developer board:
 
 Optional but recommended:
 - [Waveshare QR code scanner](https://www.waveshare.com/barcode-scanner-module.htm)
-- Long-ish pin headers like [these](https://eu.mouser.com/ProductDetail/Samtec/DW-02-10-T-S-571?qs=sGAEpiMZZMvlX3nhDDO4AE5PKXAQeC6NPk%2FcLBS9yKI%3D) to connect the scanner to the board
+- Long-ish pin headers like [these](https://eu.mouser.com/ProductDetail/Samtec/DW-02-10-T-S-571?qs=sGAEpiMZZMvlX3nhDDO4AE5PKXAQeC6NPk%2FcLBS9yKI%3D) or [these](https://www.amazon.com/gp/product/B015KA0RRU/) to connect the scanner to the board
 
 Check out the assembly video [on youtube](https://youtu.be/1H7FqG_FmCw)