Add similar figure to that found in GMTs nearneighbor documentation

pygmt/src/nearneighbor.py

@@ -50,6 +50,15 @@ def nearneighbor(x=None, y=None, z=None, data=None, **kwargs):
  criteria and :math:`r_i` is the distance from the node to the *i*'th data
  point. If no data weights are supplied then :math:`w_i = 1`.
 
+ .. figure:: https://docs.generic-mapping-tools.org/latest/_images/GMT_nearneighbor.png
+ :width: 300 px
+ :align: center
+
+ Search geometry includes the search radius (R) which limits the points
+ considered and the number of sectors (here 4), which restricts how points inside
+ the search radius contribute to the value at the node. Only the closest point
+ in each sector (red circles) contribute to the weighted estimate.
+
  Takes a matrix, xyz triples, or a file name as input.
 
  Must provide either ``data`` or ``x``, ``y``, and ``z``.