Add new contributor under the current pull request

[Piedone]

Is your feature request related to a problem? Please describe.
When asking the bot to add a new contributor in a comment under a pull request, it'll open a new pull request. This is unnecessary, and it'd be better to add the contributor's profile right there under the PR, i.e. together with the actual contribution.

If there's a CLA bot, it'll also cause issues by requesting the allcontributors bot to accept a CLA (like here, though the CLA bot's comment vanished for some reason).

Describe the solution you'd like
Add the contributor as a new commit under the current pull request.

Describe alternatives you've considered
We usually close the new PR and merge its branch into the original contribution's branch. This works, but it's a chore.

Additional context
I don't have any more.

[1408eduardo]

Hi, Do you know how to deploy blockchains?

[Piedone]

Bitcoin will fix this issue too!