Update README.md

2 spellings fixes

README.md

@@ -5,9 +5,9 @@ USB stack for embedded devices in Rust.
 
 The UsbDevice object represents a composite USB device and is the most important object for
 application implementors. The UsbDevice combines a number of UsbClasses (either custom ones, or
-pre-existing ones provided by other crates) and a UsbBus device drives to implement the USB device.
+pre-existing ones provided by other crates) and a UsbBus device driver to implement the USB device.
 
-The UsbClass trait can be used to implemented USB classes such as a HID device or a serial port. An
+The UsbClass trait can be used to implement USB classes such as a HID device or a serial port. An
 implementation may also use a custom class if the required functionality isn't covered by a standard
 class.