You can attach a Note to a sharepoint item by using Tags & Notes tool in sharepoint.
Official definitions of Tags & Notes:
“Tags help you remember links and classify the selected item. Notes are public comments. Tags and notes post to your news feed and work across different sites”
Adding a Note to a sharepoint item
Select a sharepoint item that you want to add a Note, for example a document in document library.
Select Tags & Notes from the List/Document Tab in the ribbon.
Select Note Board Tab and start typing your note.
Click Post to Add your note.
You can manage your notes in the same popup window or in Tags & Notes page. To Edit a Note click on Edit link and change your note and click Post to save your changes.
To delete a note click on Delete link and press OK to delete the note.