asterisk-asterisk/doc/README.txt

The vast majority of the Asterisk project documentation has been moved to the
project documentation:

    https://docs.asterisk.org/

Asterisk uses the Doxygen documentation software.  Run "make progdocs" and open
the resulting documentation index at doc/api/index.html in a webbrowser or copy
the directory to a directory served by a webserver for remote access.