Add chunktuner to Natural Language Processing section

[shantanu-deshmukh]

Adds chunktuner to the Natural Language Processing section, appended per project contribution rules.

Why NLP section

• Text processing for ML pipelines: chunking is a core preprocessing decision for embedding-based retrieval; data scientists building RAG need tooling beyond classic tokenizers.
• Python + PyPI: consistent with other libraries in this awesome list.
• Evaluation focus: complements DS practice of measuring model/pipeline quality rather than guessing chunk sizes.