meson: Fix build system integration bugs, add docs.

This should account for the open issues on !8 and also documents the
ninja-options that is introduced to address @ouwerkerk's recommendation.

Test suite passes and I continue to be able to build 2048.cpp. I've also
validated that ninja-options is passed to ninja when building 2048.cpp,
though this was a manual verification.
2 jobs for <span class="ref-name">feature-meson-support</span> in 1 minute and 9 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #4637
smoke-test

00:01:09

passed #4636
unit-test

00:00:34