Heba Waly authored Nov 17, 2019 and Junio C Hamano committed Nov 18, 2019

Move the documentation from Documentation/technical/api-sigchain.txt
to sigchain.h as it's easier for the developers to find the usage
information beside the code instead of looking for it in another doc file.

Also documentation/technical/api-sigchain.txt is removed because the
information it has is now redundant and it'll be hard to keep it up to
date and synchronized with the documentation in the header file.

Signed-off-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>