DOC: Add how to guide on setting number of threads in Pardiso solver #1730

Idea or request for content:

Create a new page in the How to Guide on how we can set the number of threads in a Pardiso solver.

Something similar to the instructions from this thread (requires to be logged in to Mattermost):

Try to pass solver_opts={"n_threads": 120} instead. Through solver_opts we are passing extra arguments to the solver class we choose through the solver argument, in this case Pardiso. The Pardiso class takes n_threads as argument to define how many threads should be used. See this for more details: https://github.com/simpeg/pymatsolver/blob/5b71ac426d744450676950fe68dae3c9c6044ee0/pymatsolver/direct/pardiso.py#L9-L41