Completion of the SciML Documentation Overhaul

[ChrisRackauckas]

The following are the major steps to complete the SciML documentation overhaul:

• Finish fixing up the materials for the SciML workshop (First major setup of the workshop materials SciMLWorkshop.jl#7), and add it to the SciML docs
• Add the SciML workshop to the landing page of the SciML docs, and to the Github organization README
• Create a system for downstream documentation build testing #104
• Buildkite-Based Documentation Deployments #106
• Finish writing Integrals tutorial for SciML getting started (me)
• Finish writing fitting tutorial for SciML getting started (me)
• Finishing up the showcase #93 (me)
• Turn DiffEqGPU doc examples into runnable
• Turn HighDimPDE doc examples into runnable
• Turn DeepEquilibriumNetworks doc examples into runnable
• Setup SciMLSensitivity like Reorganize the documentation ModelingToolkit.jl#1993 (me)
• Convert each example of https://github.com/ChrisRackauckas/universal_differential_equations into examples for SciMLSensitivity
• Simplify the getting started page of DifferentialEquations by using the tips in Reorganize the documentation ModelingToolkit.jl#1993 (me)

[ChrisRackauckas]

Turn DeepEquilibriumNetworks doc examples into runnable

@avik-pal can you try to do that within the next week?