Dockerfile, settable port

* added Dockerfile
* server listenting port is configurable via CLI argument

Dockerfile

@@ -0,0 +1,19 @@
+FROM alpine:3.15.0
+
+RUN apk add --no-cache git go && \
+    mkdir /oko-server && \
+    cd /oko-server && \
+    git clone https://github.com/Cernobor/oko-server.git /oko-server/git && \
+    cd /oko-server/git && \
+    go build && \
+    cp /oko-server/git/oko-server /oko-server/ && \
+    cd /oko-server && \
+    rm -rf /oko-server/git && \
+    mkdir /data && \
+    apk del git go && \
+    rm -rf /root/go && \
+    echo -e '#!/bin/sh\n/oko-server/oko-server "$@"' > /oko-server/entrypoint.sh && \
+    chmod +x /oko-server/entrypoint.sh
+VOLUME ["/data"]
+
+ENTRYPOINT ["/oko-server/entrypoint.sh"]