Remove board. in README

`from board import *`, so let's change board.SCL/board.SDA -> SCL/SDA

Author: brentru

README.rst

@@ -45,7 +45,7 @@ Next, initialize the I2C bus object:
 .. code-block:: python
 
     from board import *
-    i2c_bus = busio.I2C(board.SCL, board.SDA, frequency=100000)
+    i2c_bus = busio.I2C(SCL, SDA, frequency=100000)
 
 Since we have the I2C bus object, we can now use it to instantiate the SGP30 object:
 
@@ -116,4 +116,4 @@ Now, once you have the virtual environment activated:
 
 This will output the documentation to ``docs/_build/html``. Open the index.html in your browser to
 view them. It will also (due to -W) error out on any warning like Travis will. This is a good way to
-locally verify it will pass.
+locally verify it will pass.