Add bio and update description

Co-authored-by: Ken Jin <kenjin4096@gmail.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: hugovk

content/authors/ken-jin.json

@@ -1,6 +1,6 @@
 {
     "name": "Ken Jin",
-    "bio": "",
+    "bio": "Ken Jin is a Python core team member since Aug 2021. He works primarily on Python's performance.",
     "github": "Fidget-Spinner",
     "avatar": "",
     "twitter": "",

content/posts/jit-on-track/index.md

@@ -2,7 +2,7 @@
 title: Python 3.15's JIT is now back on track
 publishDate: '2026-03-23'
 author: Ken Jin
-description: 'The penultimate 3.15 alpha is out!'
+description: 'A look at Python's JIT in 3.15a7.'
 tags:
   - JIT
   - performance