Add docs about reproducible builds

[Cardosaum]

Overview

Users should understand what's the concept of a reproducible build, why is it important, how do we achieve reproducibility etc.

Tasks to be done

• Write a new page on the dev docs about reproducible builds
  • Should be under "Writing your zkVM application" section (the in depth explanations about the zkVM)
• Explain what is the a reproducible build
• Explain why is the reproducibility of the guest code important
• Explain how we achieve reproducibility (mention we need docker for it, cargo is not deterministic by default etc)
• Explain how users can build their ELFs in a reproducible way (mention cargo risczero build, cargo risczero deploy and also risc0_build if they want to build elfs from rust code)

[linear]

ZKVM-403 Add docs about reproducible builds

[pdg744]

transferring this from dev rel board to platform board