Update build config, add riscv build script

build_riscv64.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+# requires cargo cross (cargo install cross)
+cross build --release --all --target riscv64gc-unknown-linux-gnu 
+
+./utils/package_release.py ./target/riscv64gc-unknown-linux-gnu/release/ --output openjam_servers_linux_riscv64gc.zip