All kernel document now are changed to rst format

which means the links of all *.txt link is invalid now

The issue is about broken links in the book's documentation after a format change from .txt to .rst. Start by finding all .txt file references in the repository, likely in markdown or rst files. Use grep or a script to locate them, then update each link to point to the corresponding .rst file. Verify by building the documentation locally to ensure links work.

Written by the indexing model from the issue text.