[Docs] Added USB documentation (#6036)

Summary

Added USB documentation.

Closes: #5784

docs/source/api/usb_msc.rst

@@ -0,0 +1,114 @@
+#######
+USB MSC
+#######
+
+About
+-----
+
+USB Mass Storage Class API. This class makes the device accessible as a mass storage device and allows you to transfer data between the host and the device.
+
+One of the examples for this mode is to flash the device by dropping the firmware binary like a flash memory device when connecting the ESP32 to the host computer.
+
+APIs
+****
+
+begin
+^^^^^
+
+This function is used to start the peripheral using the default MSC configuration.
+
+.. code-block:: arduino
+
+    bool begin(uint32_t block_count, uint16_t block_size);
+
+Where:
+
+* ``block_count`` set the disk sector count.
+* ``block_size`` set the disk sector size.
+
+This function will return ``true`` if the configuration was successful.
+
+end
+^^^
+
+This function will finish the peripheral as MSC and release all the allocated resources. After calling ``end`` you need to use ``begin`` again in order to initialize the USB MSC driver again.
+
+.. code-block:: arduino
+
+    void end();
+
+vendorID
+^^^^^^^^
+
+This function is used to define the vendor ID.
+
+.. code-block:: arduino
+
+    void vendorID(const char * vid);//max 8 chars
+
+productID
+^^^^^^^^^
+
+This function is used to define the product ID.
+
+.. code-block:: arduino
+
+    void productID(const char * pid);//max 16 chars
+
+productRevision
+^^^^^^^^^^^^^^^
+
+This function is used to define the product revision.
+
+.. code-block:: arduino
+
+    void productRevision(const char * ver);//max 4 chars
+
+mediaPresent
+^^^^^^^^^^^^
+
+Set the ``mediaPresent`` configuration.
+
+.. code-block:: arduino
+
+    void mediaPresent(bool media_present);
+
+onStartStop
+^^^^^^^^^^^
+
+Set the ``onStartStop`` callback function.
+
+.. code-block:: arduino
+
+    void onStartStop(msc_start_stop_cb cb);
+
+onRead
+^^^^^^
+
+Set the ``onRead`` callback function.
+
+.. code-block:: arduino
+
+    void onRead(msc_read_cb cb);
+
+onWrite
+^^^^^^^
+
+Set the ``onWrite`` callback function.
+
+.. code-block:: arduino
+
+    void onWrite(msc_write_cb cb);
+
+Example Code
+------------
+
+Here is an example of how to use the USB MSC.
+
+FirmwareMSC
+***********
+
+.. literalinclude:: ../../../libraries/USB/examples/FirmwareMSC/FirmwareMSC.ino
+    :language: arduino
+
+.. _USB.org: https://www.usb.org/developers