A couple of typos in the arch spec

[gal-pressman]

There's a couple of typos worth fixing in the arch spec, I would submit a PR but there's no source for the PDF.

In the "Why PSP" section:

PSP uses an AEAD (Authenticated Encryption with Associated Data) method
with allows exposing things like the source and destination port numbers in
cleartext, which in turn enables firewalling/routing without decryption by
intermediate nodes in the network and richer network monitoring based on
packet sampling.

"with" -> "which".

In the "PSP Architecture -> Security Association (SA)" section:

Crypt Offset specifying the amount of packet after the IV allowed to be cleartext (but still
authenticated) when operating in AES-GCM mode

"packet" -> "bytes".