tweak gwinc keyword argument for plotting

Use 'plot' instead of 'fig', which can be confused with matplotlib
figure.

and update README
3 jobs for 13-need-side-project-with-baseline-environment in 2 minutes and 18 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #86439
test

00:02:06

 
  Deploy
passed #86440
pages

00:00:12

passed pages:deploy

00:00:00