Fix the name of the gls method, since it no longer computes strictl…

…y global strain (#180)

- Also add missing docstring for `half` arg

vital/utils/image/us/measure.py

@@ -397,7 +397,7 @@ def endo_epi_control_points(
 
     @staticmethod
     @auto_cast_data
-    def gls(
+    def longitudinal_strain(
         segmentation: T,
         lv_labels: SemanticStructureId,
         myo_labels: SemanticStructureId,
@@ -411,6 +411,8 @@ def gls(
                 ED instant.
             lv_labels: Labels of the classes that are part of the left ventricle.
             myo_labels: Labels of the classes that are part of the myocardium.
+            half: The half of the endocardium to consider when computing the strain. `None` to compute a global strain,
+                and either "left" or "right" to compute local strain.
             voxelspacing: Size of the segmentation's voxels along each (height, width) dimension (in mm).
 
         Returns: