Tidy up Workshop page

[jnewbery]

I think we can tidy up the workshops page https://bitcoinops.org/workshops/.

Suggestions:

• start with a more general introduction on our workshops, and then have summary details of the SF workshop below
• emphasize that the workshops are Chatham House rules to encourage open and candid conversations, but that general findings may be published and fed back to the open source community (we've already had two requests to info@ asking for recordings/streamings, which is a reasonable request. It'd be helpful to explain our reasoning for not offering those).
• add a call to action.
  • companies to be involved
  • companies to host
  • open source developers to attend (or perhaps speak if we change the format)
  • suggestions for locations/topics

[jnewbery]

@moneyball @jamesob we should do this, possibly after we've decided on our future workshop vision next week.