move relevant docs from RFDs 48, 61 into Omicron (#6206)

Author: davepacheco

README.adoc

@@ -14,7 +14,7 @@ Omicron is open-source. But we're pretty focused on our own goals for the forese
 
 https://docs.oxide.computer/api[Docs are automatically generated for the public (externally-facing) API] based on the OpenAPI spec that itself is automatically generated from the server implementation.  You can generate your own docs for either the public API or any of the internal APIs by feeding the corresponding OpenAPI specs (in link:./openapi[]) into an OpenAPI doc generator.
 
-There are some internal design docs in the link:./docs[] directory.
+There are some internal design docs in the link:./docs[] directory.  You might start with link:./docs/control-plane-architecture.adoc[].
 
 For more design documentation and internal Rust API docs, see the https://rust.docs.corp.oxide.computer/omicron/[generated Rust documentation].  You can generate this yourself with: