Updates the discussion of prepareProposal in the go tutorials to mention tx_max_bytes limitation to transaction set size.
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#### PR checklist
- [x] Tests written/updated, or no tests needed
- [x] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [x] Updated relevant documentation (`docs/`) and code comments, or no
documentation updates needed
(cherry picked from commit ba84060b07)
Co-authored-by: Lasaro Camargos <lasaro@informal.systems>
1ddbfa62a7