add markers for used and unused texts ind .txt files

data/ai/gpt2_poem.txt

data/ai/gpt2_sport.txt

data/ai/gpt2_wiki.txt

data/ai/gpt4o_poem.txt

data/ai/gpt4o_sports.txt

data/ai/gpt4o_wiki.txt

data/ai/opt_poem.txt

data/ai/opt_sport.txt

data/ai/opt_wiki.txt

data/human/poetry.txt.txt

data/human/sport_bbc.txt.txt

data/human/wiki.txt.txt