Add description on limitations on platforms etc.

[natterangell]

Describes some of the issues involved due to lack of future microcode updates for supported ThinkPads and how this relates to binary blobs and transient execution vulnerabilities.

This meant as a start to request made here.

[tlaurion]

@natterangell missing for thinkpads: EC controller blob, upgraded only per proprietary upgrade prior of Heads flash on proprietary firmware (outside of SPI flash).

Not required but still true: firmware in the controllers of our hardrives if not using OpenSSD project. (Nobody known to use this academic project).

[natterangell]

@tlaurion I added a section on the EC. Forgive me if I clutter the history, I am new to git. Let me know if amending and force-pushing is not the preferred way to handle edits like this.

[tlaurion]

@natterangell thanks!