docs(spi_connection): Explain which flash chips are supported

Closes espressif#1015

Author: radimkarnis

docs/en/esptool/advanced-options.rst

@@ -71,14 +71,18 @@ Passing ``--no-stub`` will disable certain options, as not all options are imple
     Overriding SPI Flash Connections
     --------------------------------
 
-    The optional ``--spi-connection`` argument overrides the SPI flash connection configuration on ESP32. This means that the SPI flash can be connected to other pins, or esptool can be used to communicate with a different SPI flash chip to the default.
+    The optional ``--spi-connection`` argument overrides the SPI flash connection configuration on {IDF_TARGET_NAME}. This means that the SPI flash can be connected to other pins, or esptool can be used to communicate with a different SPI flash chip to the default.
 
     Supply the ``--spi-connection`` argument after the ``esptool.py`` command, ie ``esptool.py flash_id --spi-connection HSPI``.
 
+    .. note::
+
+        Only NOR flash chips that are capable of at least Dual I/O (DIO) mode for SPI communication are supported. SPI NAND flash chips, as well as other types of memory devices that do not meet this requirement, are not supported.
+
     Default Behavior
     ^^^^^^^^^^^^^^^^
 
-    If the ``--spi-connection`` argument is not provided, the SPI flash is configured to use :ref:`pin numbers set in efuse <espefuse-spi-flash-pins>`. These are the same SPI flash pins that are used during a normal boot.
+    If the ``--spi-connection`` argument is not provided, the SPI flash is configured to use :ref:`pin numbers set in eFuse <espefuse-spi-flash-pins>`. These are the same SPI flash pins that are used during a normal boot.
 
     The only exception to this is if the ``--no-stub`` option is also provided. In this case, efuse values are ignored and ``--spi-connection`` will default to ``--spi-connection SPI`` unless set to a different value.