Add build timing

[davepl]

Just adds a line to the readme

• [X] I read the contribution guidelines in CONTRIBUTING.md.
• [X] I understand the BlinkenPerBit metric, and maximized it in this PR.
• [X] I selected main as the target branch.
• [X] All code herein is subjected to the license terms in COPYING.txt.

[rbergen]

"Other brands of 96-core systems are available." :)