message: add missing documentation for clippy
diff: @@ -292,6 +292,7 @@ impl<'a, F: PrimeField> CairoStep<'a, F> {
  }
  }
  +/// This struct stores the needed information to run a program
  pub struct CairoProgram<'a, F: PrimeField> {
  /// full execution memory
  mem: &'a mut CairoMemory<F>,
  