Add script for finding block closest to given date

Useful for manual grant cycle management.

scripts/find-block-for-date.js

@@ -0,0 +1,19 @@
+const promptly = require('promptly');
+const EthDater = require('ethereum-block-by-date');
+const initKredits = require('./helpers/init_kredits.js');
+
+module.exports = async function(callback) {
+  let kredits;
+  try { kredits = await initKredits(web3); } catch(e) { callback(e); return; }
+
+  const dater     = new EthDater(kredits.provider);
+  const dateStr   = await promptly.prompt('Specify a date and time (e.g. 2021-05-07T14:00:40Z): ');
+  const blockData = await dater.getDate(dateStr, true);
+
+  console.log(`
+The closest block is #${blockData.block}:
+https://rinkeby.etherscan.io/block/${blockData.block}
+`);
+
+  callback();
+}