Doc Issue: screws needed

[zruncho3d]

Reported by DrawnToLife on Discord:

sorry - now that I've done most of the conversion (A/B blocks built, extrusions swapped out, just putting the gantry back together now but idlers and what not are in place), let me clarify

the original A/B blocks use all M3x35, so you actually need 6 new new M3x30 screws to build the new A/B blocks, not just 2 (b/c you can't salvage any screws from any of the other conversion steps)