Switch to GitHub Release from CHANGELOG.md

[termoshtt]

Release note generator of GitHub becomes mature.
https://docs.github.com/en/repositories/releasing-projects-on-github/managing-releases-in-a-repository

[termoshtt]

0.15.0 has been released with GitHub release note semi-auto generation (fixed manually a bit).
https://github.com/rust-ndarray/ndarray-linalg/releases/tag/ndarray-linalg-v0.15.0

Setting of generation is here https://github.com/rust-ndarray/ndarray-linalg/blob/master/.github/release.yml