From there, I’d take a look at the canonical Webmention page of the IndieWeb wiki which has a huge number of resources. Since it looks like you’re coming from a Ruby perspective, you might appreciate the Ruby page on the IndieWeb wiki which has some pre-existing resources which may cut back on your work and learning curve. Perhaps Jason Garber (@jgarber)might be a useful resource within the Ruby world?
There is also an open source project called Silo.pub that provides a micropub endpoint for services like Tumblr, WordPress.com, Blogger, and Twitter (among others). Aaron Parecki has a public version I’m sure he wouldn’t mind if you tried.
Other platforms could quickly allow the functionality and so much more by building their own micropub servers, which would be a major boon to the social media space and the open web.
If you have questions about implementation while building, feel free to pop into the IndieWeb #dev chat (where prior implementers and others) are available for help. (Alternate chat modalities including Slack and IRC are available if you prefer.)
To get started quickly, just to have the notifications, you might try creating an account with Webmentions.io and put the endpoint into the
<head> of your site so you can receive them in the erstwhile on a separate service and worry about direct integration at a later date. As I recall Aaron Gustafson has a Webmention.io Jekyll Plugin for display and some of the outline is covered in this recent article by Max Böck.
If necessary, you can get help in the #Dev channel of the IndieWeb chat.