Performance docs

[jpn--]

Documentation updates to explain how users can tune ActivitySim models for decent performance.

[dhensle]

I think we need a recommended checklist or something similar for people that are handed a model and data and want to run it performantly on a new server. This would probably be something like:

1. run sharrow compile with a small hh sample size and save the sharrow cache to be used in subsequent runs
2. run memory profiling with a 10% or so sample to determine memory requirements
3. configure chunking if necessary
4. Run full sample in multiprocessing with 10 cores
5. Experiment with number of cores and threads to find the best performance.

[i-am-sijia]

In addition to David's comments. I'd like to add:

• We did a lot of memory and run time profiling in phase 9A. It would be nice to add an Example Model Performance section in the user docs to document the example 1-zone and 2-zone model performance.
• Recommend setting sharrow: test to catch components that are sharrow incompatible if a region is running sharrow for the first time with their model. It will be helpful to give some guidance on how to find the problematic expressions. It be helpful to also document some example incompatible expressions and how to fix them, e.g., move them into preprocessor.

[jpn--]

• We did a lot of memory and run time profiling in phase 9A. It would be nice to add an Example Model Performance section in the user docs to document the example 1-zone and 2-zone model performance.

I will open another PR with a summary of performance results and a description of the new two "canonical" examples.

[jpn--]

I believe I have addressed all the review comments. @dhensle @i-am-sijia

[i-am-sijia]

Looks great!