add docker-compose file

this will make builds generally easier

```
podman-compose up # builds
podman start -a tf2-patches-build # rebuilds :)
```

Author: getchoo

docker-compose.yml

@@ -0,0 +1,12 @@
+version: "3.9"
+
+services:
+  build:
+    environment:
+      - CCACHE_DIR=/ccache
+    image: registry.gitlab.steamos.cloud/steamrt/scout/sdk/i386
+    container_name: tf2-patches-build
+    volumes:
+      - ./:/build:z
+      - ./ccache:/ccache:z
+    entrypoint: /build/build.sh