libreoffice architecture doc is corrupt

[jodh-intel]

PR #543 added the architecture doc, including file docs/architecture/architecture-diagrams.odp. However, that file cannot be opened with libreoffice, which reports it as corrupt.

[grahamwhaley]

Hmm, does it need to be marked as a bin maybe ... unsure from my git-foo, but that would be my initial thought.
If you need me to give it a try, let me know.

[jodh-intel]

Unclear - the file is a valid zip file in a git clone but it just won't open.

@egernst - do you still have a copy of the original file? OOI did you create on Linux/Windows/Mac? Did you use libreoffice or openoffice? As it's a valid zip file, we could pick it all apart but that could get tedious :)