Add histogram gallery example (GenericMappingTools#1272)

Gallery example of a histogram with red bars on a gray background.
Elevation counts are binned at 5m intervals, and the data is
generated from a normal distribution with random noise added.

Co-authored-by: Dongdong Tian <[email protected]>
Co-authored-by: Wei Ji <[email protected]>
Co-authored-by: Will Schlitzer <[email protected]>

examples/gallery/histograms/histogram.py

@@ -0,0 +1,37 @@
+"""
+Histogram
+---------
+The :meth:`pygmt.Figure.histogram` method can plot regular histograms.
+Using the ``series`` parameter allows to set the interval for the width of
+each bar. The type of histogram (frequency count or percentage) can be
+selected via the ``histtype`` parameter.
+"""
+
+import numpy as np
+import pygmt
+
+np.random.seed(100)
+
+# generate random elevation data from a normal distribution
+mean = 100  # mean of distribution
+stddev = 25  # standard deviation of distribution
+data = mean + stddev * np.random.randn(521)
+
+fig = pygmt.Figure()
+
+fig.histogram(
+    table=data,
+    # define the frame, add title and set background color to
+    # lightgray, add annotations for x and y axis
+    frame=['WSne+t"Histogram"+glightgray', 'x+l"Elevation (m)"', 'y+l"Counts"'],
+    # generate evenly spaced bins by increments of 5
+    series=5,
+    # use red3 as color fill for the bars
+    fill="red3",
+    # use a pen size of 1p to draw the outlines
+    pen="1p",
+    # choose histogram type 0 = counts [default]
+    histtype=0,
+)
+
+fig.show()