Adding first example to svMultiPhysics User Guide

[justran-csuf]

Current situation

This pull request is the first example to be added to the CFD User Guide. It contains a worked example of setting up a steady rigid wall simulation in a patient-specific geometry of the descending aorta and iliac artery. It goes through the logical steps one would take to set up a CFD simulation along with the necessary commands in the svMultiPhysics .XML input file needed to execute these. Explanations are added to give context as to why certain decisions are made as well as to teach users the basics of CFD and cardiovascular modeling. Simulation results are also discussed briefly to show users what they should be looking for.

Release Notes

• Created a whole new page in the "documentation" folder called "svmp_user_guide" that has all of the markdown files needed for the example. Style of the markdown files was created using the style guide provided (i.e. creating separate folders for each markdown file, naming each file "readme.md", etc.)
• Created a new HTML file within "documentation" that follows the provided template that displays all markdown files in the same page
• User guide has not been linked to any other page in the documentation. It is currently in the review stage.

Documentation

• This pull request only adds files to the "documentation" folder. No existing files have been modified.

Testing

• Tested using the "Live Server" feature in Visual Studio and appears to look fine.

Code of Conduct & Contributing Guidelines

• I agree to follow the Code of Conduct and Contributing Guidelines.

[ktbolt]

@justran-csuf The CFD User Guide content should be placed under simvascular.github.io/documentation/multi_physics/user-guide with the other user guide content

cardiac_electrophysiology/	hemodynamics/			nonlinear_solid_dynamics/
fluid_solid_interaction/	material_models/		readme.md

[alisonmarsden]

I think now that we are only supporting one solver, it makes sense to document how to run simulations with all the different physics one may want to use: CFD, EP, mechanics, etc. All of these will now be done with svMultiPhysics. Some of this content is already in the "SimCardio" section, so we should break that up and move the content to the relevant sections (for example there is quite a nice description there on how to run an EP simulation which needs to be updated). See the google slide I sent a while back with a possible outline. We could have a header on running simulations with svMultiPhycis, and in the main menu then list all the different physics options in an easy to find manner.