add x86 manual

[sollyucko]

x86 is the most commonly-used architecture for most software currently, so therefore a specification of it would be quite valuable to include. Here are some useful links to find the document:

• https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
• https://cdrdv2.intel.com/v1/dl/getContent/671200
• https://www.lulu.com/spotlight/intelsdm