Minor documentation mismatch in atom ordering (protein.py vs residue_constants.py)

[Monikerton]

I noticed a small inconsistency between the atom ordering described in protein.py and the actual ordering in residue_constants.py.

In protein.py:

# Cartesian coordinates of atoms in angstroms. The atom types correspond to
# residue_constants.atom_types, i.e. the first three are N, CA, CB.
atom_positions: np.ndarray  # [num_res, num_atom_type, 3]

But in residue_constants.py:

atom_types = [
    "N",
    "CA",
    "C",
    "CB",
 ...

so CB is the 4th item in the atom_types array, not the third.

Fix would just be to change the comment from N, CA, CB to N, CA, C.