sysroot.proto: Clarification in doc block.

BUG=chromium:1124093
TEST=./generate.sh

Change-Id: I44fa38b402f5666851ac46796df7d666564215ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2391118
Tested-by: Alex Klein <saklein@chromium.org>
Auto-Submit: Alex Klein <saklein@chromium.org>
Reviewed-by: Navil Perez <navil@google.com>
Commit-Queue: Navil Perez <navil@google.com>
2 files changed