chore(ci): ensure new rules include README changes

Author: noahbenham

dangerfile.js

@@ -7,3 +7,10 @@ const { danger, fail } = require('danger');
 if (danger.github.pr.body.length === 0) {
   fail('Please include a body for your PR');
 }
+
+if (
+  danger.git.created_files.find(filename => filename.startsWith('rules/')) &&
+  !danger.git.modified_files.includes('README.md')
+) {
+  fail('Please update the README when new rules are added');
+}