[docs] Update SUMMARY.md

Adds the following sections to md-book:

* Specification documents
* Design documents

Signed-off-by: Miguel Osorio <[email protected]>

Author: moidx

docs/src/SUMMARY.md

@@ -4,10 +4,26 @@
 
 # User Guide
 
-- [Getting Started](./getting-started.md)
-- [Usage](./usage.md)
+* [Getting Started](./getting-started.md)
+* [Usage](./usage.md)
+
+# Specification
+
+* [Introduction](./specification/README.md)
+* [Firmware Resiliency](./specification/firmware_resiliency.md)
+* [Middleware](./specification/middleware/README.md)
+  * [MCTP](./specification/middleware/mctp.md)
+  * [SPDM](./specification/middleware/spdm.md)
+  * [PLDM](./specification/middleware/pldm.md)
+* [Services](./specification/services/README.md)
+* [Device Abstraction](./specification/device_abstraction/README.md)
+* [Terminology](./specification/terminology.md)
 
 # Developer Guide
 
-- [Architecture](./architecture.md)
-- [Contributing](./contributing.md)
+* [Architecture](./architecture.md)
+* [Contributing](./contributing.md)
+* [Design](./design/README.md)
+  * [Digest Driver for Hubris](./design/driver-hubris-hash.md)
+  * [Rust Traits to IDL Guide](./design/rust-trait-to-idl-conversion.md)
+

docs/src/design/README.md

@@ -0,0 +1 @@
+# Design