Add support for NPM packages

Adding an NPM package.json file allows the NuCypher contracts to be
treated as an NPM package, which facilitates the import of the contracts
in Node.js frameworks such as Hardhat.

Author: manumonti

package.json

@@ -0,0 +1,7 @@
+{
+  "name": "nucypher-contracts",
+  "version": "0.0.1",
+  "license": "AGPL-3.0-or-later",
+  "description": "NuCypher Network Smart Contracts",
+  "author": "NuCypher"
+}