README named --experimental-strip-types, which was renamed to
--strip-types. Document the current flag only.
The extension recommendations list is unchanged, but the VSCode section
undercounted it and now matches extensions.json. The per-language
formatter blocks in .vscode/settings.json stay (they keep a user's
local formatter settings from overriding the project's) and gain the
JSX/TSX language ids to match what oxfmt and the lefthook glob cover.