docs: add security review preparation checklist

[sylvarissolutions-max]

Closes #113.

Converts the Trail of Bits blog post on preparing for a security audit into an actionable checklist, with the blockchain-specific additions mentioned in the issue.

What is in this PR

New file: `development-guidelines/preparing-for-a-review.md`

Organized into five sections:

1. Define the scope and goals
2. Resolve the easy issues (compiler warnings, Slither, test coverage, dead code)
3. Document the codebase (NatSpec, inline comments, prior reviews)
4. Deliver the code batteries-included (build environment, test process, deployment)
5. Blockchain-specific preparation (Slither setup, commit hashes, reviewer access, privileged roles, external dependencies)

README update: one new bullet under Development Guidelines, alphabetically placed between Incident Response and Secure Development Workflow.

Style and voice

I tried to match the existing checklists in the repo (`token_integration.md` and `review_checklist.md` were the closest references). Every item is a check-boxed imperative with a one-line rationale. I kept the language consistent with those files and avoided adding commentary that was not already in the Trail of Bits post or in the issue comments.

I incorporated the points raised in the issue thread about blockchain-specific preparation: Slither execution, commit hash pinning, reviewer access provisioning, privileged role documentation, and external dependency trust assumptions.

What is NOT in this PR

• No changes to existing checklists
• No changes to the Slither guide or other linked docs
• No new diagrams or images
• No CI or tooling changes

Happy to adjust the wording, split sections differently, move the file, or restructure if it fits better with the rest of the repo. Let me know.

[CLAassistant]

All committers have signed the CLA.