v3.0.12: Add kraken to readme, add endpoint for fetching historic bills

What's Changed

• chore(): README.md template sections by @tiagosiebler in #159
• • adds @siebly/kraken-api SDK to readme
• • adds https://siebly.io to readme
• feat(v3.0.12): add endpoint for fetching bills older than 30 days by @tiagosiebler in #160

Full Changelog: v3.0.11...v3.0.12