Add explanatory text

readme.md

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 # rust-spdm
 
-A rust version SPDM implementation.
+This project provides a Rust language implementation of [SPDM](https://www.dmtf.org/sites/default/files/standards/documents/DSP0274_1.2.1.pdf)
+and [TDISP](https://pcisig.com/tee-device-interface-security-protocol-tdisp).
+These protocols are used to facilitate direct device assignment for Trusted Execution
+Environment I/O (TEE-I/O) in Confidential Computing. 
+
+There are a number of use cases that benefit from including devices and accelerators in the trust
+boundary of a Confidential Virtual Machine (CVM). In machine learning, for example, these
+protocols can be used to build a trusted connection between a GPU’s TEE and a CVM to accelerate
+performance.
+
 
 ## Features