The file is renamed within its own directory and every markdown link in the scanned tree that
pointed at the old name is rewritten to the new one, reusing the move machinery's link
refactoring (relative-path recomputation and bystander discovery included). The file's own
content is never reformatted by this command; it reaches the new name byte-for-byte apart from
any link rewrites the shared move machinery itself performs.
Convert a README.md to index.md, or an index.md to README.md, in place.
The file is renamed within its own directory and every markdown link in the scanned tree that pointed at the old name is rewritten to the new one, reusing the move machinery's link refactoring (relative-path recomputation and bystander discovery included). The file's own content is never reformatted by this command; it reaches the new name byte-for-byte apart from any link rewrites the shared move machinery itself performs.