Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/scripts/prepare-contracts-package.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+# cd to the root of the repo
+cd "$(git rev-parse --show-toplevel)"
+
+# avoids re-compilation during publishing of both packages
+if [[ ! -v ALREADY_COMPILED ]]; then
+  npm run clean
+  npm run prepare
+  npm run prepack
+fi
+
+cp README.md contracts/
+mkdir contracts/build contracts/build/contracts
+cp -r build/contracts/*.json contracts/build/contracts