Merge pull request matplotlib#3163 from tacaswell/hist_doc

DOC : documented bottom kwarg of hist

Author: NelleV

lib/matplotlib/axes/_axes.py

@@ -5350,6 +5350,12 @@ def hist(self, x, bins=10, range=None, normed=False, weights=None,
             `True`, then the histogram is normalized such that the first bin
             equals 1.
 
+        bottom : array_like, scalar, or None, default: None
+            Location of the bottom baseline of each bin.  If a scalar,
+            the base line for each bin is shifted by the same amount.
+            If an array, each bin is shifted independently and the length
+            of bottom must match the number of bins.  If None, defaults to 0.
+
         histtype : ['bar' | 'barstacked' | 'step' | 'stepfilled'], optional
             The type of histogram to draw.