Auto merge of #3837 - Turbo87:ops-guide, r=jtgeibel

Add `create-diff-link.sh` script

Replacement for #3835 and symbiotic with https://github.com/rust-lang/crates-io-ops-guide/pull/4 :)

Author: bors

script/create-diff-link.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+set -e
+
+echo "fetching updates from production app…"
+git fetch heroku-prod
+
+prod_sha=`git rev-parse --short heroku-prod/master`
+master_sha=`git rev-parse --short master`
+
+echo ""
+echo "production app is at: ${prod_sha}"
+echo "local \`master\` branch is at: ${master_sha}"
+echo ""
+echo "https://github.com/rust-lang/crates.io/compare/${prod_sha}...${master_sha}"