Add contours to docs and README feature matrix (#964)

Author: brendancol

README.md

@@ -255,6 +255,7 @@ In the GIS world, rasters are used for representing continuous phenomena (e.g. e
 | Name | Description | NumPy xr.DataArray | Dask xr.DataArray | CuPy GPU xr.DataArray | Dask GPU xr.DataArray |
 |:-----|:------------|:------------------:|:-----------------:|:---------------------:|:---------------------:|
 | [Polygonize](xrspatial/polygonize.py) | Converts contiguous regions of equal value into vector polygons | ✅️ | ✅️ | ✅️ | 🔄 |
+| [Contours](xrspatial/contour.py) | Extracts elevation contour lines (isolines) from a raster surface | ✅️ | ✅️ | 🔄 | 🔄 |
 
 --------
 

docs/source/reference/utilities.rst

@@ -25,6 +25,13 @@ Polygonize
 
     xrspatial.polygonize.polygonize
 
+Contours
+========
+.. autosummary::
+    :toctree: _autosummary
+
+    xrspatial.contour.contours
+
 Diagnostics
 ===========
 .. autosummary::