add dockerfile + docker build step

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

Dockerfile

@@ -0,0 +1,14 @@
+FROM alpine:latest AS build
+
+RUN apk --no-cache add ca-certificates
+
+FROM scratch
+# needed for version check HTTPS request
+COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+
+# create the /tmp dir, which is needed for image content cache
+WORKDIR /tmp
+
+COPY syft /
+
+ENTRYPOINT ["/syft"]