add doc + add port to containerfile

Containerfile

@@ -2,4 +2,5 @@ FROM scratch
 ARG BUILT_ARTIFACT
 ADD "$BUILT_ARTIFACT" /
 ENTRYPOINT [ "/nftables-exporter" ]
+EXPOSE 9923/tcp
 CMD [ ]

README.md

@@ -2,4 +2,16 @@
 
 A prometheus exporter that exposes nftables counters.
 
-**WORK IN PROGRESS**
+## Usage
+
+Create some counters.
+
+```sh
+sudo ./test.nft
+```
+
+Run the exporter.
+
+```sh
+sudo podman run -d --rm --name nftables-exporter --network host --cap-drop all --cap-add net_admin quay.io/itix/nftables-exporter:latest
+```