fix: add dockerfile

Dockerfile

@@ -0,0 +1,17 @@
+# Production image based on alpine.
+FROM alpine
+LABEL maintainer="Lukas Malkmus <mail@lukasmalkmus.com>"
+
+# Upgrade packages and install ca-certificates.
+RUN apk update --no-cache \
+    apk upgrade --no-cache \
+    apk add --no-cache ca-certificates
+
+# Copy binary into image.
+COPY tankerkoenig_exporter /usr/bin/tankerkoenig_exporter
+
+# Use the project name as working directory.
+WORKDIR /tankerkoenig_exporter
+
+# Set the binary as entrypoint.
+ENTRYPOINT [ "/usr/bin/tankerkoenig_exporter" ]