revised prompt formatter source to reflect new tutorial 5 name

docs/source/prompt_formatter.rst

@@ -2,7 +2,7 @@ Prompt Formatter
 ================
 
 A Prompt Formatter object deals with formatting prompts for specific tasks, such as 
-cell type generation and cell type prediction.
+cell generation and cell type prediction.
 
 
 .. autofunction:: prompt_formatter.get_cell_sentence_str