update docstring

Author: bw4sz

docs/user_guide/01_Reading_data.md

@@ -139,14 +139,14 @@ shp = utilities.read_file(input="/path/to/boxes_shapefile.shp")
 shp.head()
 ```
 
-If your shapefile does not include an `image_path` column, you must provide the raster path via `rgb_path`:
+If your shapefile does not include an `image_path` column, you must provide the raster path via `img_path`:
 
 ```python
 from deepforest import utilities
 
 shp = utilities.read_file(
     input="/path/to/boxes_shapefile.shp",
-    rgb_path="/path/to/OSBS_029.tif"
+    image_path="/path/to/OSBS_029.tif"
 )
 ```
 
@@ -157,7 +157,7 @@ from deepforest import utilities
 
 shp = utilities.read_file(
     input="/path/to/boxes_shapefile.shp",
-    rgb_path="/path/to/OSBS_029.tif",
+    image_path="/path/to/OSBS_029.tif",
     label="Tree"
 )
 ```