use markdown

Change-Id: I286e325ec573def0728dd6deeefc134b5dbc75e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/build/empty-project/+/3278451
Reviewed-by: Lizzy Presland <zland@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/README b/README.md
similarity index 100%
rename from README
rename to README.md