Update paper link

Fix broken link.

architecture/README.md

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 This spec document defines the IPFS protocol stack, the subsystems, the interfaces, and how it all fits together. It delegates non-interface details to other specs as much as possible. This is meant as a top-level view of the protocol and how the system fits together.
 
-Note, this document is not meant to be an introduction of the concepts in IPFS and is not recommended as a first pass to understanding how IPFS works. For that, please refer to the [IPFS paper](https://github.com/ipfs/specs/tree/master/papers/ipfs.pdf).
+Note, this document is not meant to be an introduction of the concepts in IPFS and is not recommended as a first pass to understanding how IPFS works. For that, please refer to the [IPFS paper](https://github.com/ipfs/papers/raw/master/ipfs-cap2pfs/ipfs-p2p-file-system.pdf).
 
 # Table of Contents