Update HTML layout and language attributes

[vertuevanguardin-lgtm]

• Have you followed the contributing guidelines?
• Have you explained what your changes do, and why they add value to the Guides?

Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

---

[vertuevanguardin-lgtm]

Clone and checkout the branch

git clone https://github.com/github/opensource.guide.git
cd opensource.guide
git checkout patch-1

Fix 1: Restore index.html front matter

cat > index.html << 'EOF'

layout: index
lang: en

EOF

Fix 2: Update broken link in best-practices.md

Replace line 226:

FROM: — @edunham, "Rust's Community Automation"

TO: — @edunham, "Rust's Community Automation"

Fix 3: Update broken link in finding-users.md

Replace line 112:

FROM: — Lena Reinhard, "How to Prepare and Write a Tech Conference Talk"

TO: — Lena Reinhard, "How to Prepare and Write a Tech Conference Talk"

Commit and push

git add index.html _articles/best-practices.md _articles/finding-users.md
git commit -m "Fix: Restore YAML front matter and update broken external links"
git push origin patch-1