Add 0.41.0 prerelease notes and unignore docs

Add comprehensive NumSharp 0.41.0-prerelease release notes at docs/releases/RELEASE_0.41.0-prerelease.md describing the IL Kernel Generator, SIMD improvements, new APIs, bug fixes, performance gains, tests, and installation/testing instructions. Update .gitignore to ensure docs/releases/ is not ignored so the release notes are tracked.

Author: Nucs

.gitignore

@@ -360,3 +360,4 @@ docs/DESIGN.md
 
 # Claude Code worktrees (local only)
 .claude/worktrees/
+!docs/releases/