Add HAND and TWI to README feature matrix (#954) (#955)

Both functions were already implemented but missing from the
Hydrology section of the feature matrix.

Author: brendancol

README.md

@@ -278,6 +278,8 @@ In the GIS world, rasters are used for representing continuous phenomena (e.g. e
 | [Stream Link](xrspatial/stream_link.py) | Assigns unique IDs to each stream segment between junctions | ✅️ | ✅️ | ✅️ | 🔄 |
 | [Snap Pour Point](xrspatial/snap_pour_point.py) | Snaps pour points to the highest-accumulation cell within a search radius | ✅️ | ✅️ | 🔄 | 🔄 |
 | [Flow Path](xrspatial/flow_path.py) | Traces downstream flow paths from start points through a D8 direction grid | ✅️ | ✅️ | 🔄 | 🔄 |
+| [HAND](xrspatial/hand.py) | Computes Height Above Nearest Drainage by tracing D8 flow to the nearest stream cell | ✅️ | ✅️ | 🔄 | 🔄 |
+| [TWI](xrspatial/twi.py) | Topographic Wetness Index: ln(specific catchment area / tan(slope)) | ✅️ | ✅️ | ✅️ | 🔄 |
 
 -----------