Added vaa clarifications

[ilariae]

Description

Added clarifications about vaas and reorgs

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[nonergodic]

Please read the whitepaper that Evan linked.

There's still all sorts of verbiage in here that suggests that consistency levels represent "number of block confirmations" when this is not true any longer.
e.g.

The consistency level you set on the emitting contract determines how many confirmations the Guardians await before attesting a message.

or

However, if your use case strictly requires guaranteed uniqueness for each emitted message, configure a higher consistency level even in the event of reorgs.

(but there is no higher commitment level than finalized)