VCF-50: Update region_partition and sample_partition parameter descriptions (#869)

* Updated region_partition and sample_partition parameter descriptions

Author: alancleary

apis/python/src/tiledbvcf/dataset.py

@@ -47,9 +47,11 @@
 limit : int
     Max number of records (rows) to read
 region_partition : tuple
-    Region partition tuple (idx, num_partitions)
+    Region partition tuple (idx, num_partitions) partitions regions into
+    num_partitions partitions and only reads regions from partition idx (0-based)
 sample_partition : tuple
-    Samples partition tuple (idx, num_partitions)
+    Samples partition tuple (idx, num_partitions) partitions samples into
+    num_partitions partitions and only reads samples from partition idx (0-based)
 sort_regions : bool
     Whether or not to sort the regions to be read, default True
 memory_budget_mb : int