Resolve three leftover TODOs in wp/sections/introduction.tex

[Arinapakalova]

There are three unaddressed TODO comments in the introduction section of the paper:

1. Line 26: % (\todo: examples!!). — Needs examples of functional quality quantification.
2. Line 31: %\todo: refs. — Needs a reference supporting the claim about maintainability being hard to quantify.
3. Line 33: % (\todo: ref). — Needs a reference regarding domains where functional correctness outweighs maintainability.

These TODOs should be resolved by adding the missing text and relevant academic references.