docs: add troubleshooting guide

[buihoangthai]

Summary

Added troubleshooting notes for node setup.

Changes

• Added Windows setup notes
• Added common installation issues
• Improved developer onboarding

Testing

Documentation only.

[buihoangthai]

Thanks for reviewing. I added these notes based on issues I encountered while setting up a node, hoping it helps new node operators avoid common setup problems .

[osr21]

The intent here is good — node setup troubleshooting genuinely helps new operators — but the current content is too generic to be actionable. None of the bullet points include a specific command, error message, config value, or version number, so a reader hitting an actual failure can't use them to diagnose anything.

A few concrete items from real Arc Testnet development that would fit a troubleshooting section (and aren't covered elsewhere in the README yet):

Chain ID mismatch in wallet / tooling config
Arc Testnet is 5042002 (0x4cef52). Several third-party chain registries and older guides circulate 1516. If MetaMask or a JSON-RPC client is rejecting the chain or signing for the wrong network, verify the chain ID directly:

curl -s -X POST https://rpc.testnet.arc.network     -H "Content-Type: application/json"     -d '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}' | jq .result
# Expected: "0x4cef52"

RPC endpoint availability
rpc.testnet.arc.network is the documented primary but can be intermittently slow. rpc.drpc.testnet.arc.network has been more reliable as a primary in practice. Configure both if your client supports fallback RPC lists.

Block explorer URLs
testnet.arcscan.app is the canonical explorer. explorer.testnet.arc.network is unreachable and explorer.arc.io is team-login-gated — both circulate in older guides and wallet configs but neither works for external users.

eth_estimateGas for complex calls
Gas estimation on Arc Testnet returns unreliable values for multi-step contract calls (e.g. receiveMessage on the CCTP MessageTransmitter). If transactions revert with an out-of-gas error that does not reproduce on other chains, override gasLimit explicitly (600 000 covers most cases) rather than relying on estimation.

These are specific enough that a reader can act on them. Happy to submit a follow-up PR with this content if it would be useful — or the author can incorporate whichever items are relevant here.