add welcome bot

[RayStick]

Closes #

Proposed Changes

• Added welcome bot (this has already been implanted in other repos, see here for explanation and see here for implementation in phys2bids - it is the exact same config.yml file being added)

Change Type

• bugfix (+0.0.1)
• minor (+0.1.0)
• major (+1.0.0)
• refactoring (no version update)
• test (no version update)
• infrastructure (no version update)
• documentation (no version update)
• other

Checklist before review

• I added everything I wanted to add to this PR.
• [Code or tests only] I wrote/updated the necessary docstrings.
• [Code or tests only] I ran and passed tests locally.
• [Documentation only] I built the docs locally.
• My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• My code respects the adopted style, especially linting conventions.
• The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• I added or indicated the right labels.

• I added information regarding the timeline of completion for this PR.

• Please, comment on my PR while it's a draft and give me feedback on the development!

[RayStick]

@all-contributors add @RayStick for infrastructure

[allcontributors]

@RayStick

I've put up a pull request to add @RayStick! 🎉

[RayStick]

@all-contributors add @me-pic for review

[allcontributors]

@RayStick

I've put up a pull request to add @me-pic! 🎉