How do I add Webmentions to my site?

You can integrate web mentions into Blot but it will require a little work. There are two articles, kindly written by others, which should guide you through the process:

• Displaying Webmentions with Posts by Amit Gawande
• Enabling webmentions on a Blot-hosted blog by Matthew Finlayson.

I've not used webmentions myself but please let me know if you have any questions about this implementation

Thanks for your reply which brings me another question: do you know if this is compatible with using a commenting service like Commento or it must be one or the other?

Technically speaking, I don't see why you couldn't embed both Commento and webmentions on one page – I think it would be up to your judgement whether or not it would be practically suitable on your site