update readme, prevent speed <=0

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>

add cli args: -n and -speed

Both accept an int. n is the number of flakes

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>

make animations slightly smoother

The previous drawing would advance some flakes by 3 rows per draw cycle.
Smooth this out by advancing 1 row at a time, but at different
frequencies

minor comment update, use already created window for vt.Draw

add readme

initial commit