Add TDX Attestation

[yogeshbdeshpande]

rendered at https://github.com/veraison/docs/blob/intel-tdx-musings/musings/intel-tdx-attestation.md

[setrofim]

Real nice write-up, just a few minor nits. In addition to the comments on specific lines -- there appear to be a few lines (mainly in the glossary, but also a few elsewhere) that aren't wrapped to the same column width as the rest of the document.