Moved files into separate folders per 'en' and 'zh_CN' language version and linked 'zh_CN' files back to 'en' files if translation is not yet available

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

@@ -0,0 +1,23 @@
+System API
+**********
+
+.. toctree::
+   :maxdepth: 1
+
+   FreeRTOS <freertos>
+   FreeRTOS Hooks <hooks>
+   Heap Memory Allocation <mem_alloc>
+   Heap Memory Debugging <heap_debug>
+   Interrupt Allocation <intr_alloc>
+   Watchdogs <wdts>
+   Inter-Processor Call <ipc>
+   High Resolution Timer <esp_timer>
+   Logging <log>
+   Application Level Tracing <app_trace>
+   Power Management <power_management>
+   Sleep Modes <sleep_modes>
+   Base MAC address <base_mac_address>
+   Over The Air Updates (OTA) <ota>
+
+
+Example code for this API section is provided in :example:`system` directory of ESP-IDF examples.