Suggested build step fails

[Vtec234]

The README instructs to run

lake exe generate-manual --depth 2

but on a fresh checkout (f447334) this fails with

uncaught exception: No source found for tutorials. Errors encountered:
 * no such file or directory (error code: 4294967294)
  file: /Users/wjn/reference-manual/_tutorial-out/xref.json

[medovina]

I'm seeing this too. Apparently you must first run

$ lake exe generate-tutorials

and then

$ lake exe generate-manual --depth 2