spec: updates per internal feedback

[redshiftzero]

Describe your changes

This PR contains protocol spec changes from internal feedback

Issue ticket number and link

Related to #4280
Closes #4342

Checklist before requesting a review

• If this code contains consensus-breaking changes, I have added the "consensus-breaking" label. Otherwise, I declare my belief that there are not consensus-breaking changes, for the following reason:

  spec only

[TalDerei]

@redshiftzero we have so many good talks / presentations about penumbra, but none of them are linked in our protocol spec / blog posts / etc. I think they should be made more available somehow. Maybe a dedicated section for this, or peppered throughout the spec based on their relevance, etc.

• https://www.youtube.com/watch?v=ziUZyQmHh4c&ab_channel=ZeroKnowledge
• https://www.youtube.com/watch?v=xYZBv_lFhMI&ab_channel=Nebular
• https://www.youtube.com/watch?v=JjmOelgfqNo&ab_channel=EthereumFoundation
• https://www.youtube.com/watch?v=1-RKOR_k4IQ&ab_channel=GatewaytoCosmos
• https://www.youtube.com/watch?v=-ap9ja36EYU&ab_channel=ZeroKnowledge
• https://www.youtube.com/watch?v=-ap9ja36EYU&ab_channel=ZeroKnowledge
• https://www.youtube.com/watch?v=EEUKPrno3u4&ab_channel=Nebular
• https://www.youtube.com/watch?v=mHoe7lQMcxU&ab_channel=ZeroKnowledge
• https://www.youtube.com/watch?v=Mq67m98yW0E&ab_channel=TheInterop
• https://www.youtube.com/watch?v=Mq67m98yW0E&ab_channel=TheInterop
• https://www.youtube.com/watch?v=-DC8gbZo_NQ&ab_channel=ForesightInstitute
• https://www.youtube.com/watch?v=PfFTHWJWmOs&t=1s&ab_channel=ZeroKnowledge
• https://www.youtube.com/watch?v=3_y2dcHNeF0&ab_channel=ZeroKnowledge

here's just some of the one's I've watched for instance. I don't personally know much about comms or the best way to expose these.

cc @hdevalence

[hdevalence]

I'm not sure these should go in the protocol spec but they would be a great addition to the Respurces section of the guide!