New construction guide with minor changes

[Ember]

The more workshops I conduct, the better I understand the Gray-B-Gon,
and the minor changes in the construction guide dated 17 July arise
from that. It's in the Files section.

1. Metal brackets attached to masts with 1" screws instead of 1-5/8"
screws (whose points stuck out from some 2x2's.)

2. Axle short piece is now 2-1/2" rather than 2". Step 15, cutting
PVC axle pieces, has a revised and I think simpler process.

3. Drum lacing with zigzag twine is the same, but easier.

4. The pvc pipe in the pulley is now 1" long rather than 7/8".

5. Step 19 now mentions work-hardening as something to avoid when
lacing the copper wire.

6. Step 25, building the drive belt, has a better description of the
knotting, and a slightly better knot.