[Docs] README payout instructions say Base — bounties pay test USDC on ARC Testnet

I will pay for a fixed file - details below. ## Bug (docs) [`README.md`](https://github.com/Hazyshades/Sendly-Test-Repo/blob/main/README.md) Contributing section ends with: *"Include your Base payout address in the PR description when requested."* All active bounties now pay **test USDC on ARC Testnet**, so contributors are instructed to submit addresses on the wrong network. ## Acceptance criteria - [ ] Contributing section describes the ARC-testnet-USDC claim flow (/attempt -> PR -> post ARC EVM address after merge) - [ ] Bounty cases table mentions reward currency (test USDC, ARC Testnet) - [ ] No remaining Base-payout references ## Reward I will pay **15 USDC (test tokens)** on **ARC Testnet** for a merged fix — same flow as #53, but payout is test USDC on ARC, not Base. How to claim: 1. Comment `/attempt` with this issue number before you start. 2. Open a PR referencing this issue (`Fixes #`). 3. After the PR is reviewed and merged, comment your **ARC testnet EVM address** here — you receive 15 test USDC on ARC.