Docstrings
Summary:
- scalar: extend docstring of secp256k1_scalar_set_b32
- field: extend docstring of secp256k1_fe_normalize
This is a backport of secp256k1 PR713
Test Plan:
make check
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D5388