DOC: Clarify Coords Report Example

- add remark that this only pertains to the interactive backend
- PEP8 fixes

Author: StefRe

examples/misc/coords_report.py

@@ -3,22 +3,23 @@
 Coords Report
 =============
 
-Override the default reporting of coords.
+Override the default reporting of coords as the mouse moves over the axes
+in an interactive backend.
 """
 
 import matplotlib.pyplot as plt
 import numpy as np
 
 
 def millions(x):
-    return '$%1.1fM' % (x*1e-6)
+    return '$%1.1fM' % (x * 1e-6)
 
 
 # Fixing random state for reproducibility
 np.random.seed(19680801)
 
 x = np.random.rand(20)
-y = 1e7*np.random.rand(20)
+y = 1e7 * np.random.rand(20)
 
 fig, ax = plt.subplots()
 ax.fmt_ydata = millions