docs(testing): document link-checker binary release process

Add comprehensive documentation for maintainers on how to:
- Create releases in docs-tooling (automated)
- Manually distribute binaries to docs-v2 (required for private repo)
- Update workflow references when needed

This addresses the missing process documentation for link-checker
binary distribution between the two repositories.

Author: jstirnaman

TESTING.md

@@ -171,6 +171,47 @@ cargo build --release
 cp target/release/link-checker /usr/local/bin/
 ```
 
+#### Binary Release Process
+
+**For maintainers:** To create a new link-checker release in docs-v2:
+
+1. **Create release in docs-tooling** (builds and releases binary automatically):
+   ```bash
+   cd docs-tooling
+   git tag link-checker-v1.2.x
+   git push origin link-checker-v1.2.x
+   ```
+
+2. **Manually distribute to docs-v2** (required due to private repository access):
+   ```bash
+   # Download binary from docs-tooling release
+   curl -L -H "Authorization: Bearer $(gh auth token)" \
+     -o link-checker-linux-x86_64 \
+     "https://github.com/influxdata/docs-tooling/releases/download/link-checker-v1.2.x/link-checker-linux-x86_64"
+   
+   curl -L -H "Authorization: Bearer $(gh auth token)" \
+     -o checksums.txt \
+     "https://github.com/influxdata/docs-tooling/releases/download/link-checker-v1.2.x/checksums.txt"
+   
+   # Create docs-v2 release
+   gh release create \
+     --repo influxdata/docs-v2 \
+     --title "Link Checker Binary v1.2.x" \
+     --notes "Link validation tooling binary for docs-v2 GitHub Actions workflows." \
+     link-checker-v1.2.x \
+     link-checker-linux-x86_64 \
+     checksums.txt
+   ```
+
+3. **Update workflow reference** (if needed):
+   ```bash
+   # Update .github/workflows/pr-link-check.yml line 98 to use new version
+   sed -i 's/link-checker-v[0-9.]*/link-checker-v1.2.x/' .github/workflows/pr-link-check.yml
+   ```
+
+> [!Note]
+> The manual distribution is required because docs-tooling is a private repository and the default GitHub token doesn't have cross-repository access for private repos.
+
 #### Core Commands
 
 ```bash