doc: update docstring

Author: msto

fgpyo/sam/__init__.py

@@ -578,7 +578,16 @@ def parse_sa_tag(tag: str) -> List["SupplementaryAlignment"]:
 
     @classmethod
     def from_read(cls, read: pysam.AlignedSegment) -> List["SupplementaryAlignment"]:
-        """Returns a list of SupplementaryAlignments for a given pysam.AlignedSegment."""
+        """
+        Construct a list of SupplementaryAlignments from the SA tag in a pysam.AlignedSegment.
+
+        Args:
+            read: An alignment. The presence of the "SA" tag is not required.
+
+        Returns:
+            A list of all SupplementaryAlignments present in the SA tag.
+            If the SA tag is not present, or it is empty, an empty list will be returned.
+        """
         if read.has_tag("SA"):
             sa_tag: str = cast(str, read.get_tag("SA"))
             return cls.parse_sa_tag(sa_tag)