Small documentation update.

docs/apis/api.md

docs/data/upload.md

docs/develop/code.md

docs/explanation/architecture.md

docs/explanation/architecture.png

docs/explanation/basics.md

docs/explanation/data.md

docs/explanation/data.png

docs/explanation/datamodel.png

docs/explanation/oasis-use-cases.png

docs/explanation/oasis.md

docs/explanation/schema.png

docs/explanation/schema_language.png

docs/explanation/screenshot.png

docs/explanation/stack.png

docs/explanation/super_structure.png

docs/index.md

docs/schemas/basics.md

docs/tutorial/access_api.md

docs/tutorial/custom.md