docs: fix typo and step 3 rendering in arc-multichain-wallet README

[alelpoan]

Fix a typo and broken rendering in the README.

Changes:

• README.md: "transfering" → "transferring" in image alt text
• README.md: add blank line after step 3 heading to fix rendering

Test plan
Documentation-only change; no code paths affected.

[Sertug17]

+1 — verified locally. Independently noticed the same transfering
→ transferring typo while looking at this repo. Same word is
already spelled correctly on README:145 ("When transferring USDC
cross-chain...") and in components/wallet-dashboard.tsx:559,
so this is clearly an unintentional typo.

The step 3 rendering fix is a nice bonus catch as well 👍

Cross-repo context: while reviewing the Arc sample apps I also
filed/saw a few related cleanups — the chain config in
lib/circle/gateway-sdk.ts had decimals: 6 and a broken
explorer URL across multiple apps, addressed in:

• arc-multichain-wallet#37 by @Ccheh (this repo)
• arc-fintech#21 by me

Hopefully these all get a review soon — clean PRs sitting open.