reflect i2c bus passing

Author: turbinenreiter

README.md

@@ -26,7 +26,10 @@ If you have any questions, open an issue.
 Example:
 ```python
 from bmp180 import BMP180
-bmp180 = BMP180()
+from machine import I2C, Pin                        # create an I2C bus object accordingly to the port you are using
+bus = I2C(1, I2C.MASTER, baudrate=100000)           # on pyboard
+# bus =  I2C(scl=Pin(4), sda=Pin(5), freq=100000)   # on esp8266
+bmp180 = BMP180(bus)
 bmp180.oversample_sett = 2
 bmp180.baseline = 101325