added costs basis tool to the Payouts FAQ

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 038b3e3):

https://storj-docs--pr411-add-costs-basis-tool-5sem7pjf.web.app

_{(expires Mon, 15 Jul 2024 05:26:39 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

_{Sign: 3c1f0a7f83da2cd749f45c4149016bdb4af1841c}

[storjrobot]

This pull request has been mentioned on Storj Community Forum (official). There might be relevant details there:

https://forum.storj.io/t/june-6-2024-may-payouts-complete/26494/8