add intro numpy example

Basic intro exercise for numpy. The example images are in the repo under data/ @stamper @ralves @ext.bauer - happy for review from anyone!

_episodes/02-data.md

@@ -35,19 +35,20 @@ keypoints:
     - include an aside about I/O - reading/writing files (pandas (the `.to_*()` methods and highlight some: `csv`, `json`, `feather`, `hdf`), numpy, `open()`, (?) bytes vs strings, (?) encoding)
   - Finish with example of `df.plot()` to set the scene for plotting section
   
-> ## Reading data to a numpy array
-> We'll use the popular image analysis package scikit-image, to read two example images into numpy
-> arrays.
-> > ~~~
-> > from skimage.io import imread
-> > raw = imread('cilliated_cell.png')
-> > nuclei = imread('cilliated_cell_nuclei.png')
-> > # if you want to see what these images look like - we can use matplotlib (more to come later!)
-> > import matplotlib.pyplot as plt
-> > plt.imshow(raw, cmap='gray')
-> > plt.imshow(nuclei)
-> > ~~~
-> > {: .language-python }
+## Reading data to a numpy array
+We'll use the popular image analysis package scikit-image, to read two example images into numpy
+arrays.
+~~~
+from skimage.io import imread
+raw = imread('cilliated_cell.png')
+nuclei = imread('cilliated_cell_nuclei.png')
+# if you want to see what these images look like - we can use matplotlib (more to come later!)
+import matplotlib.pyplot as plt
+plt.imshow(raw, cmap='gray')
+plt.imshow(nuclei)
+~~~
+{: .language-python }
+> ## Exploring Image Arrays
 > * What are the dimensions of these arrays?
 > * What data type are these arrays?
 > * What is the minimum and maximum value of these arrays?