Add Chinese translation for the rst documents in storage folder, including:

1. docs/zh_CN/api-reference/storage/fatfs.rst
2. docs/zh_CN/api-reference/storage/index.rst
3. docs/zh_CN/api-reference/storage/sdmmc.rst
4. docs/zh_CN/api-reference/storage/spiffs.rst
5. docs/zh_CN/api-reference/storage/wear-levelling.rst

docs/en/api-reference/storage/fatfs.rst

@@ -1,6 +1,8 @@
 FAT Filesystem Support
 ======================
 
+:link_to_translation:`zh_CN:[中文]`
+
 ESP-IDF uses the `FatFs <http://elm-chan.org/fsw/ff/00index_e.html>`_ library to work with FAT filesystems. FatFs resides in the ``fatfs`` component. Although the library can be used directly, many of its features can be accessed via VFS, using the C standard library and POSIX API functions.
 
 Additionally, FatFs has been modified to support the runtime pluggable disk I/O layer. This allows mapping of FatFs drives to physical disks at runtime.

docs/en/api-reference/storage/index.rst

@@ -1,6 +1,8 @@
 Storage API
 ***********
 
+:link_to_translation:`zh_CN:[中文]`
+
 .. toctree::
     :maxdepth: 1
 

docs/en/api-reference/storage/spiffs.rst

@@ -1,6 +1,8 @@
 SPIFFS Filesystem
 =================
 
+:link_to_translation:`zh_CN:[中文]`
+
 Overview
 --------