Enable Gitpod links in pull requests by default?

[jankeromnes]

@akosyakov Thanks for releasing this bot!

It looks super useful, but I’m a bit surprised that it doesn’t do anything by default. Adding Gitpod links to all Pull Requests is such a killer feature that I’d expect it to do that by default once installed on a repository (like any other GitHub App, e.g. Reviewable, Travis, CircleCI, etc. they all perform default actions once they're installed). Instead, I just installed an App that doesn’t do anything, and I need to add yet another config file to my repository to fix that…

Bug steps:

• install gitpod-bot for your repository
• open a new pull request on this repository

Expected behavior:

• gitpod-bot should add a Gitpod link to the new pull request
• you can optionally configure any non-standard behavior by adding a config file to your repository

Actual behavior:

• installing gitpod-bot doesn't do anything by default (no link appears in new pull requests)
• you must perform an extra step: add yet another config file to your repository, in order to make the bot do useful things

(My suggestion makes that config file optional by default, which is great for lazy people like myself.)