docs/zh_CN: move process related docs into process dir

docs/zh_CN: move process related docs into process dir

Much process documents spread here isn't neat. It's good to put them together
in their directory: process

So create 'process' directory and move docs:
	email-clients stable_kernel_rules stable_api_nosense
	submittingpatches submittingdrivers HOWTO
	volatile-considered-harmful
there.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Harry Wei <harryxiyou@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Coly Li <colyli@suse.de>
Signed-off-by: Weiwei Jia <harryxiyou@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>