Add inline example for grdtrack (#1725)

Co-authored-by: Michael Grund <23025878+michaelgrund@users.noreply.github.com>
Co-authored-by: Dongdong Tian <seisman.info@gmail.com>
Co-authored-by: Meghan Jones <meghanj@alum.mit.edu>

pygmt/src/grdtrack.py

@@ -12,6 +12,8 @@
     use_alias,
 )
 
+__doctest_skip__ = ["grdtrack"]
+
 
 @fmt_docstring
 @use_alias(
@@ -264,6 +266,22 @@ def grdtrack(points, grid, newcolname=None, outfile=None, **kwargs):
           ``outfile`` is not set
         - None if ``outfile`` is set (track output will be stored in file set
           by ``outfile``)
+
+    Example
+    -------
+    >>> import pygmt
+    >>> # Load a grid of @earth_relief_30m data, with an x-range of -118 to
+    >>> # -107, and a y-range of -49 to -42
+    >>> grid = pygmt.datasets.load_earth_relief(
+    ...     resolution="30m", region=[-118, -107, -49, -42]
+    ... )
+    >>> # Load a pandas dataframe with ocean ridge points
+    >>> points = pygmt.datasets.load_sample_data(name="ocean_ridge_points")
+    >>> # Create a pandas dataframe from an input grid and set of points
+    >>> # The output dataframe adds a column named "bathymetry"
+    >>> output_dataframe = pygmt.grdtrack(
+    ...     points=points, grid=grid, newcolname="bathymetry"
+    ... )
     """
     if hasattr(points, "columns") and newcolname is None:
         raise GMTInvalidInput("Please pass in a str to 'newcolname'")