add Dockerfile

To keep things consistent with other mautrix-xxx bridges

Dockerfile

@@ -0,0 +1,21 @@
+FROM golang:1-alpine3.20 AS builder
+
+RUN apk add --no-cache git ca-certificates build-base su-exec olm-dev
+
+COPY . /build
+WORKDIR /build
+
+RUN go build -o /usr/bin/mautrix-slack ./cmd/mautrix-slack
+
+FROM alpine:3.20
+
+ENV UID=1337 \
+    GID=1337
+
+RUN apk add --no-cache ffmpeg su-exec ca-certificates olm bash jq yq-go curl
+
+COPY --from=builder /usr/bin/mautrix-slack /usr/bin/mautrix-slack
+COPY --from=builder /build/docker-run.sh /docker-run.sh
+VOLUME /data
+
+CMD ["/docker-run.sh"]