Add `activitypub-core`

Update README

README.md

@@ -336,6 +336,8 @@ Emoji's for each entry provide additional information on project status:
 
 #### Other
 
+* [**activitypub-core**](https://github.com/michaelcpuckett/activitypub-core): An attempt to build a spec-compliant ActivityPub server in Node.js. `MIT, TypeScript`
+
 * [**Alovoa**](https://github.com/Alovoa/alovoa) ([site](https://alovoa.com/)): Free and open-source dating platform that respects your privacy (considering AP support, see [issue](https://github.com/Alovoa/alovoa/issues/13)) `AGPL-3.0, Java`
 
 * [**Communecter**](https://github.com/pixelhumain/communecter) ([site](https://www.communecter.org/)): Manage cities as a connected citizen, produce openCityData, manage organizations, projects, events openly, an open societal approach (intends to add AP support, see [this issue](https://github.com/pixelhumain/communecter/issues/1395)) `Apache-2.0, PHP`