Update init/README.md to mention bootconfig for androidboot argument

In Android S and later, androidboot.* kernel cmdline parameters are
moved to bootconfig instead the kernel cmdline. This includes the
androidboot.force_normal_boot.

Bug: 219951268
Test: N/A
Change-Id: Id0328ad09a34d654de9936e37a576a8a9f44de6c
1 file changed