DeepChem Updates of November, 2023 (Week 3)

Here is a quick summary of DeepChem updates for the 3rd week of November, including the following merged pull requests:

1. AddXC [Basexc Helper class]: This PR introduces the AddXC helper class, providing a new feature, and includes documentation modifications.

2. LinearOperator Base Class: This PR introduces the base class for Linear Operator, a new feature with documentation updates.