Merge branch 'documentation/systems_addition' into 'develop'

...sizing/systems_design/figures/architecture_definition.png

...ocumentation/sizing/systems_design/figures/flow-chart.jpg

...ocumentation/sizing/systems_design/figures/flow-chart.png

...ion/sizing/systems_design/figures/mission-power-ATA70.png

...ation/sizing/systems_design/figures/overall_structure.png

...ntation/sizing/systems_design/figures/power_summation.png

...mentation/sizing/systems_design/figures/system-masses.png

...umentation/sizing/systems_design/figures/system_class.png

docs/documentation/sizing/systems_design/getting-started.md

docs/documentation/sizing/systems_design/index.md

...umentation/sizing/systems_design/software_architecture.md

docs/documentation/sizing/systems_design/systems.md

mkdocs.yml