docs: enhance README with L1 RPC providers, troubleshooting, and examples

[Dark-Brain07]

Improved README documentation to help new node operators get started faster.

Changes:

Added L1 RPC Providers section with Alchemy, Infura, QuickNode, and self-hosted examples
Enhanced Quick Start with concrete configuration examples
Converted client list to comparison table with "Best For" recommendations
Expanded Troubleshooting section covering common issues:
Node startup failures
Slow sync speed
RPC connection errors
Improved Snapshots section with step-by-step restoration instructions
Why: Addresses frequent questions from Discord 🛠｜node-operators channel and reduces setup friction for new operators.

[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 1 Sum 2

[Dark-Brain07]

Thanks for the automated checks.

This PR introduces a minimal and scoped change with no impact on security-sensitive logic.
I see Heimdall is requesting a review due to repository policy and an unsigned commit.

I’m happy to re-sign the commit if required, and would appreciate a maintainer review when convenient.

Thank you for your time.