otatool: Fixes read_ota_partition cmd, required output arg

Closes: https://github.com/espressif/esp-idf/issues/6559

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

@@ -288,7 +288,7 @@ The command-line interface of `otatool.py` has the following structure:
   otatool.py --port "/dev/ttyUSB1" switch_ota_partition --slot 1
 
   # Read OTA partition 'ota_3' and save contents to a file named 'ota_3.bin'
-  otatool.py --port "/dev/ttyUSB1" read_ota_partition --name=ota_3
+  otatool.py --port "/dev/ttyUSB1" read_ota_partition --name=ota_3 --output=ota_3.bin
 
 
 More information can be obtained by specifying `--help` as argument:

docs/zh_CN/api-reference/system/ota.rst

@@ -269,7 +269,7 @@ Python API
   otatool.py --port "/dev/ttyUSB1" switch_ota_partition --slot 1
 
   # 读取 OTA 分区 'ota_3'，将内容保存至文件 'ota_3.bin'
-  otatool.py --port "/dev/ttyUSB1" read_ota_partition --name=ota_3
+  otatool.py --port "/dev/ttyUSB1" read_ota_partition --name=ota_3 --output=ota_3.bin
 
 
 更多信息可用 `--help` 指令查看：