Bundle bouncer at build time, add versioning, update docs

Dockerfile

@@ -1,8 +1,32 @@
 # syntax=docker/dockerfile:1
 
+FROM ghcr.io/linuxserver/baseimage-alpine:3.20 AS buildstage
+
+ARG MOD_VERSION
+
+RUN \
+  mkdir -p /root-layer && \
+  if [[ -z "${MOD_VERSION}" ]]; then \
+    MOD_VERSION=$(curl -sX GET "https://api.github.com/repos/crowdsecurity/cs-nginx-bouncer/releases/latest" \
+    | jq -r '.tag_name'); \
+  fi && \
+  if [[ -z ${MOD_VERSION+x} ]]; then \
+    echo "**** Could not fetch current bouncer version from Github ****" \
+    exit 1; \
+  fi && \
+  curl -sLo \
+    /root-layer/crowdsec-nginx-bouncer.tgz -L \
+    "https://github.com/crowdsecurity/cs-nginx-bouncer/releases/download/${MOD_VERSION}/crowdsec-nginx-bouncer.tgz" && \
+  if ! tar -tzf /root-layer/crowdsec-nginx-bouncer.tgz >/dev/null 2>&1; then \
+    echo "**** Invalid tarball, could not download crowdsec bouncer ****" \
+    exit 1; \
+  fi
+
+COPY root/ /root-layer/
+
 FROM scratch
 
 LABEL maintainer="thespad"
 
-# copy local files
-COPY root/ /
+# Add files from buildstage
+COPY --from=buildstage /root-layer/ /