fix jsonl_to_markdown

[ved1beta]

Fixes #162

Changes proposed in this pull request:

• Add jsonl_to_markdown.py utility script to convert JSONL files to Markdown format
• Script extracts the 'text' field from each line in a JSONL file and saves it as a separate Markdown file
• Include proper error handling for JSON decoding and file operations
• Add example usage and documentation

Before submitting

• [x] I've read and followed all steps in the Making a pull request section of the CONTRIBUTING docs.
• [x] I've updated or added relevant docstrings following the syntax described in the Writing docstrings section of the CONTRIBUTING docs.
• [x] If this PR fixes a bug, I've added a test that will fail without my fix.
• [x] If this PR adds a new feature, I've added tests that sufficiently cover my new functionality.

fixes #162