Fix links in DESIGN.md

DESIGN.md

 # Kubernetes Overview
 
-See the [user overview](docs/overview.md) for an introduction to Kubernetes and its core concepts.
+See the [user guide overview](docs/user-guide/overview.md) for an introduction to Kubernetes and its core concepts.
 
 See the [design overview](docs/design) for an overview of the system design.
 
-See the [API overview](docs/api.md) and [conventions](docs/api-conventions.md) for an overview of the API design.
+See the [API overview](docs/api.md) and [conventions](docs/devel/api-conventions.md) for an overview of the API design.
 
 
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