fix doc bug and add a little extra

Author: dhalbert

README.rst

@@ -30,7 +30,7 @@ bundle <bundle_installation>`.
 To install:
 
 #. Download and unzip the `latest release zip <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/releases>`_.
-#. Copy the unzipped ``adafruit_bus_device`` to the ``lib`` directory on the ``CIRCUITPY`` or ``MICROPYTHON`` drive.
+#. Copy the unzipped ``adafruit_bus_device`` to the ``lib`` directory on the ``CIRCUITPY`` drive.
 
 API
 ---

adafruit_bus_device/spi_device.py

@@ -45,8 +45,11 @@ class SPIDevice:
             cs = digitalio.DigitalInOut(D10)
             device = SPIDevice(spi_bus, cs)
             bytes_read = bytearray(4)
+            # The object assigned to spi in the with statements below
+            # is the original spi_bus object. We are using the busio.SPI
+            # operations busio.SPI.readinto() and busio.SPI.write().
             with device as spi:
-                spi_device.readinto(bytes_read)
+                spi.readinto(bytes_read)
             # A second transaction
             with device as spi:
                 spi.write(bytes_read)