is RNG note about Mersenne Twister correct?

Section 1.3.1 seems to incorrectly indicate that the default PRNG is Mersenne not PCG64.

```
np.random: random numbers (Mersenne Twister PRNG):
```

This conflicts with the actual behavior:

```
>>> import numpy as np
>>> rng = np.random.default_rng(27446968)
>>> rng
Generator(PCG64) at 0x7FD121D4DD20
```