Add USB_FLASH_DRIVE_SUPPORT

Marlin/src/sd/usb_flashdrive/SOURCES.txt

@@ -0,0 +1,48 @@
+
+==== SUMMARY ====
+
+Source Path:                           Repository:                           License:
+------------                           -----------                           --------
+usb_flashdrive/lib                     github.com/felis/USB_Host_Shield_2.0  GPLv2 or later
+usb_flashdrive/lib/masstorage.cpp [1]  github.com/greiman/UsbFat             MIT
+usb_flashdrive/lib/settings.h [1]      github.com/greiman/UsbFat             MIT
+
+[1] Changes related to SKIP_WRITE_PROTECT and DELAY only
+
+
+==== USB HOST SHIELD 2.0 LIBRARY ====
+
+The lib/ folder contains a subset of the files from the USB Host Shield 2.0
+library:
+
+  https://github.com/felis/USB_Host_Shield_2.0
+
+While the original library was released under the GPLv2 and could not be
+commingled with Marlin, the developers have graciously re-licenced the
+files needed for Marlin as "GPLv2 or later", as documented in this thread.
+
+  https://github.com/felis/USB_Host_Shield_2.0/issues/364
+
+Small modifications have been made to the source. Please search for
+USB_FLASH_DRIVE_SUPPORT or look at the patch file to see what was changed.
+
+
+==== PERFORMANCE ENHANCEMENTS FOR USB DRIVES ====
+
+There are also some small performance enhancements from Bill Greiman, regarding
+SKIP_WRITE_PROTECT and DELAY. These changes came from the following repo:
+
+   https://github.com/greiman/UsbFat
+
+While the original library was released under the GPLv2 and could not be
+commingled with Marlin, the developer has graciously re-licenced his changes
+under the "MIT" license, as documented here:
+
+   https://github.com/greiman/UsbFat/issues/8
+
+==== MARLIN INTEGRATION WORK ====
+
+All additional work done to integrate USB into Marlin was performed by AlephObjects, Inc.
+and is licensed under the GPLv3.
+
+-- marcio@alephobjects.com