Update activitypub-models link

[siranweb]

Firstly, thanks for adding my package to this repo :)

Want to ask you to update the activitypub-js/activitypub-models link from readme, because it's archived now. I made another package SiranWeb/activitypub-types, which is based on previous one. Probably it will be useful for people who needs to implement models logic by themselves.

Thank you!

[randName]

i stopped following the space very closely so thanks for the update!