Add explicit @ref link in dae_example.md

[abhro]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• Any new documentation only uses public API

Additional context

The link text doesn't lead to actual cross-reference link, so the target link in @ref is updated.

[abhro]

Should solve this error when building docs:

┌ Error: Cannot resolve @ref for md"[DAE Initialization documentation](@ref)" in docs/src/tutorials/dae_example.md.
│ - No docstring found in doc for binding `Base.-`.
└ @ Documenter ~/.cache/julia-buildkite-plugin/depots/0185fce3-4489-413a-a934-123dd653ef61/packages/Documenter/yVko2/src/utilities/utilities.jl:47