Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of writer],
Thank you for allowing me to take a look at [name of work]. Although I feel like you have a very promising start with this novel, I don't feel you quite have a publishable body of work here. There are certainly some very strong elements, and I did read the book all the way through.
I am very impressed with your writing ability, and feel like you could polish this up some to make it publishable. I have enclosed the entire manuscript, on which I have made suggestions and edits for a rewrite.
Should you make a substantial effort in rewriting this manuscript, I would be happy to take another look at it.
Best of luck,