from https://ariejan.net/2009/10/26/how-to-create-and-apply-a-patch-with-git/
from the branch with changes
git format-patch <branched-from> --stdout > <patch-name>.patch
go to the branch to patch
git checkout <branch-to-patch>
check the changes
git apply --stat <patch-name>.patch
test the patch
git apply --check <patch-name>.patch
apply the patch
git am --signoff < <patch-name>.patch