Make "want read" button work

internal/model/userbook.go

@@ -5,9 +5,10 @@ import "gorm.io/gorm"
 // describes the relationship between a user and a book.
 type UserBook struct {
 	gorm.Model
-	UserID uint
-	BookID uint
-	Book   Book
-	Rating int
-	Read   bool
+	UserID   uint
+	BookID   uint
+	Book     Book
+	Rating   int
+	Read     bool
+	WantRead bool
 }