docs(samples): add region tags (#788)

* docs(samples): add read table snippet

* remove snippet as it already exists

samples/hello/main.py

@@ -87,26 +87,30 @@ def main(project_id, instance_id, table_id):
 
     # [START bigtable_hw_create_filter]
     # Create a filter to only retrieve the most recent version of the cell
-    # for each column accross entire row.
+    # for each column across entire row.
     row_filter = row_filters.CellsColumnLimitFilter(1)
     # [END bigtable_hw_create_filter]
 
     # [START bigtable_hw_get_with_filter]
+    # [START bigtable_hw_get_by_key]
     print("Getting a single greeting by row key.")
     key = "greeting0".encode()
 
     row = table.read_row(key, row_filter)
     cell = row.cells[column_family_id][column][0]
     print(cell.value.decode("utf-8"))
+    # [END bigtable_hw_get_by_key]
     # [END bigtable_hw_get_with_filter]
 
     # [START bigtable_hw_scan_with_filter]
+    # [START bigtable_hw_scan_all]
     print("Scanning for all greetings:")
     partial_rows = table.read_rows(filter_=row_filter)
 
     for row in partial_rows:
         cell = row.cells[column_family_id][column][0]
         print(cell.value.decode("utf-8"))
+    # [END bigtable_hw_scan_all]
     # [END bigtable_hw_scan_with_filter]
 
     # [START bigtable_hw_delete_table]