docs: add ecosystem quick checklist to README

[GomezAdalyn]

Summary

• Add a quick checklist for projects updating the Base Ecosystem page
• Highlight the key commands and assets that should be verified before opening a PR

Rationale

• Makes it easier for builders to confirm their ecosystem entry and assets are correctly configured before submitting

[vercel]

@GomezAdalyn 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

[GomezAdalyn]

Happy to adjust the wording or table entries if you have preferred terminology for node operators