把dockerfile移动到`docker`目录，以便github workflow生效 (#5)

Dockerfile → docker/Dockerfile

@@ -7,6 +7,11 @@
 
 FROM ubuntu:22.04 as build
 
+# For CI/CD purposes, we can pass a pre-run command to the build image
+ARG PRE_RUN_CMD=""
+
+RUN $PRE_RUN_CMD
+
 RUN apt-get update -y && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
       g++ \