docs(exo): Update NEWS.md

[gibson042]

Ref #1740

Note also that we've got quite a bit of variance in NEWS.md files; should that be corrected?

$ awk 'FNR==1 && $0!=""' packages/*/NEWS.md | sort
User-visible changes in base64:
User-visible changes in `@endo/captp`:
User-visible changes in `@endo/exo`:
User-visible changes in `@endo/marshal`:
User-visible changes in `@endo/promise-kit`:
User-visible changes in eventual-send:
User-visible changes in SES:
User-visible changes in SES-Ava:
User-visible changes in Static Module Record, née Transform Module:
User-visible changes in Zip:
User-visible changes to netstring:
User-visible changes to the CommonJS module analyzer:
User-visible changes to the compartment mapper:
User-visible changes to the Endo environment initializer: