Create a GitHub App that detects first-time comments and responds with links to how to contribute

We get way too many comments from first-time visitors to Plone's repositories on GitHub who don't read the contributing guidelines. We want to point them to these guidelines before they waste their and our time. @stevepiercy patiently responds to most of these lost souls with a GitHub Saved Reply, depending on the repository as follows.

Documentation

please read and follow [First-time contributors](https://6.docs.plone.org/contributing/first-time.html), especially [Things not to do](https://6.docs.plone.org/contributing/first-time.html#things-not-to-do), [Contributing to Plone](https://6.docs.plone.org/contributing/index.html), and [Contribute to documentation](https://6.docs.plone.org/contributing/documentation/index.html). 

Volto

please read and follow [First-time contributors](https://6.docs.plone.org/contributing/first-time.html), especially [Things not to do](https://6.docs.plone.org/contributing/first-time.html#things-not-to-do), [Contributing to Plone](https://6.docs.plone.org/contributing/index.html), and [Contributing to Volto](https://6.docs.plone.org/contributing/volto.html). 

Plone

please read and follow [First-time contributors](https://6.docs.plone.org/contributing/first-time.html), especially [Things not to do](https://6.docs.plone.org/contributing/first-time.html#things-not-to-do), and [Contributing to Plone](https://6.docs.plone.org/contributing/index.html). 

It would be nice to automate this process to help these first-timers. Probot appears to have a good tutorial that could help create a bot to do this.

https://probot.github.io/docs/

The issue names no repository files or tests. Start with the Probot tutorial and the listed GitHub Saved Reply examples, then define how first-time comments and repository-specific guidance should be recognized. Done means the GitHub App responds with the appropriate contribution links for the Documentation, Volto, and Plone repositories.