message: clarification about cairo field size
diff: +/*
  + The Cairo Language works natively for field elements in the finite field with
  + modulus 0x800000000000011000000000000000000000000000000000000000000000001
  + This is the hexadecimal value for 2 ^ 251 + 17 * 2 ^ 192 + 1
  + Our Pallas curves have 256 bits, so Cairo native instructions will fit.
  +*/
  +
  // TODO(querolita):
  // - Enlarge native word type to u256
  