docs: add Base quickstart (chain IDs, minimal config, tips)

[stalim17]

Adds a Base-focused quickstart for OnchainKit to speed up onboarding.

What changed? Why?

• Added official Base chain IDs (8453 / 84532)
• Included a minimal Next.js + wagmi config snippet
• Added UX tips (auto-switch to Base, BaseScan links, RPC fallback)
  → Goal: reduce time-to-first-deploy for Base builders.

Notes to reviewers

• New doc lives at docs/base-quickstart.md
• Content is additive; no code paths or packages touched

How has it been tested?

• Config snippet validated with wagmi base / baseSepolia
• Links checked (BaseScan / RPC)

[vercel]

@stalim17 is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	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