MiSTer: create and upload supplemental meta-data 7zip archive

[tjanas]

Create and upload a 7z file that would contain readme files, config files, wallpapers, and other supplemental public domain files in the expected directory structure. These files would be merged by the end-user with the output from running build_pack. Similar to the SD System Card Structure files for the Analogue Nt Mini Noir jailbreak.

Alternatively, these files could be uploaded individually and uncompressed to add visibility and the ability to view changes in git commit diffs; they would be packaged into a 7z via creating a "release" on github.