Add docs

docs/explanation/design_philosophy.md

docs/explanation/interpolation_methods.md

docs/explanation/material_properties.md

docs/how-to/define_materials.md

docs/how-to/energy_temperature_conversion.md

docs/reference/api/alloy.md

docs/reference/api/interpolators.md

docs/reference/api/yaml_parser.md

docs/reference/yaml_schema.md

docs/tutorials/first_simulation.md

docs/tutorials/getting_started.md