doc: mention opening port 80 in AWS setup docs
doc: mention opening port 80 in AWS setup docs

Change-Id: I67a38327d634580c0e44d80491f1977cc4cd358a
Reviewed-on: https://upspin-review.googlesource.com/18580
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin