docs/zh_CN: core-api: Add generic-radix-tree Chinese translation

Translate core-api/generic-radix-tree.rst into Chinese.

Last English version used:

commit ba20ba2e3743 ("generic radix trees").

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Yanteng Si<siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/aad94e2a053ae021eb4d63240690b05c2f3e8dec.1660881950.git.zhoubinbin@loongson.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>