docs(cli): document native mise installation

[jmgilman]

Summary

• add a focused how-to for installing release-cli through mise's built-in GitHub backend
• document project, temporary, global, and local-alias configuration
• distinguish native GitHub backend support from the unavailable mise registry shorthand
• link the guide from the README and CLI/release contract references

Verification

• isolated mise use github:meigma/release@0.1.2 install selected the Darwin arm64 archive, checked it, and verified its GitHub artifact attestation
• project, mise x, global, and local-alias invocations all reported release-cli 0.1.2 at commit 611195c21fdd44ff2cf95c6a8833f84d095270b0
• mise exec -- moon run check
• git diff --check