docs(scripts): document Solana CLI prerequisite

[jackchuma]

Linear: https://linear.app/coinbase/issue/CHAIN-4912/improve-solana-bridge-quick-start-guide

What changed? Why?

The scripts quick start uses solana-keygen new without explaining how to install the required CLI. Add a link to the official Solana CLI installation instructions before that command and tell readers to install the CLI first.

Notes to reviewers

Only scripts/README.md changes. Existing commands remain unchanged. CLI installation, key generation, and bridge operations are out of scope.

How has it been tested?

• git diff --check origin/main...HEAD passes.
• The installation page returns HTTP 200. Verified its install-solana-cli anchor, Agave installer instructions, and solana --version verification command.
• No tests added for this documentation-only change. No installation, key generation, signing, or transactions were run.

Generated with Toshi

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

⚠️ Ignored Reviews (4)

Reviewer	Reason
xenoliss	Old or outdated review
0xth4nh	Soft review, as user does not have write permissions
xenoliss	Soft review, as user does not have write permissions
xenoliss	Review missing MFA

[linear]

CHAIN-4912

[0xth4nh]

LGTM !!!