Use build argument to select foundry version

Containerfile

@@ -1,4 +1,6 @@
 FROM docker.io/library/debian:stable-slim
+ARG FOUNDRY_VERSION
+ENV FOUNDRY_VERSION=${FOUNDRY_VERSION}
 # We need nodejs 14.x, we get it from upstream
 RUN apt-get update
 # xz-utils is required for decompressing '.tar.xz'
@@ -11,7 +13,7 @@ RUN useradd --system foundry --home-dir /var/lib/foundry
 RUN mkdir -p /var/lib/foundry/vtt
 RUN mkdir -p /var/lib/foundry/data
 WORKDIR /var/lib/foundry/vtt
-COPY foundryvtt.zip /root/foundryvtt.zip
+COPY FoundryVTT-${FOUNDRY_VERSION}.zip /root/foundryvtt.zip
 RUN unzip /root/foundryvtt.zip
 RUN rm /root/foundryvtt.zip
 RUN chown -R foundry: /var/lib/foundry

README.md

@@ -1,6 +1,11 @@
 # Building
 
-`podman build -t foundry .`
+1. Download foundry version to the local directory, eg. `FoundryVTT-10.285.zip`
+2. Build the container
+
+```
+podman build --build-arg FOUNDRY_VERSION=10.285 -t foundry:10.285 .
+```
 
 # First run: