chore: add generated files bot to repo (#545)

* chore: add generated files bot to repo

* chore: add template source location to bot config

Author: freelerobot

handwritten/nodejs-logging-winston/.github/generated-files-bot.yml

@@ -0,0 +1,5 @@
+# Source template: https://github.com/googleapis/synthtool/blob/master/synthtool/gcp/templates/node_library/CONTRIBUTING.md
+externalManifests:
+- type: json
+  file: 'synth.metadata'
+  jsonpath: '$.generatedFiles[*]'