Remove code_walkthrough.md from tracking and gitignore it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: erwardenaar

.gitignore

@@ -8,5 +8,6 @@ dist/
 build/
 *.deb
 docs/vignette_files/
+docs/code_walkthrough.md
 docs/code_walkthrough.html
 docs/code_walkthrough_files/