What we used to do when I worked at a consulting firm that took contracts whose deliverables included source code is when writing code just put in the comments that we needed for ourselves during development.
For the final delivery of source code we'd make a binder that had a code listing on the pages that were on the right side, with a detailed running commentary on the pages that were on the left. On the left hand pages we could go into great detail (we'd add vertical space on the right hand pages as needed to keep things lined up).
The left hand pages in essence were almost a book on how to do whatever it was the code was doing, making it easy for the client to hand over the project to their own programmers after we were gone. We did not rush writing the left hand pages. Sometimes I spent more time writing the left hand pages than I had spend writing and debugging the code. (Our contracts were all fixed bid contracts, so spending all that time didn't raise the price for the client).
For the final delivery of source code we'd make a binder that had a code listing on the pages that were on the right side, with a detailed running commentary on the pages that were on the left. On the left hand pages we could go into great detail (we'd add vertical space on the right hand pages as needed to keep things lined up).
The left hand pages in essence were almost a book on how to do whatever it was the code was doing, making it easy for the client to hand over the project to their own programmers after we were gone. We did not rush writing the left hand pages. Sometimes I spent more time writing the left hand pages than I had spend writing and debugging the code. (Our contracts were all fixed bid contracts, so spending all that time didn't raise the price for the client).