Fix README delimiter in sort.py to prevent CI README corruption

[mohiuddin-khan-shiam]

Fix README delimiter in sort.py to prevent CI README corruption

Description

sort.py expected the string "- - -" to split the README into Table-of-Contents and body, but the markdown file actually uses the standard horizontal rule ---.
This mismatch caused the script (run in CI) to mis-process the README, leading to corrupted documentation and potential IndexErrors.

Changes made:

• Replaced the obsolete delimiter with ---.
• Added a safe fallback when the delimiter is absent.
• Preserved original formatting by re-inserting the exact delimiter.

CI now runs python sort.py without errors and the README remains intact.