Add subch base network

[zhichen3]

No description provided.

[zingale]

can you add a description here about what the purpose of this network is

[zingale]

nevermind, I found it

This network is a further simplification of subch_simple by
excluding N14, F18, Ne21, and Na22.
These nuclei were added to include n14(a, g)f18(a, p)ne21 rate sequence,
which allows an enhancement to the c12(p, g)n13(a, p)o16 rate due to the
proton release. However, we find that the effect is not very significant,
and they also caused an artificial endpoint at Na22.