This fixes all links listed a broken by `yarn build`.
Incidentally, even working relative links may be listed as broken when
linking file a.md from b.md in the same folder as `[stuff from a](./a)`.
Instead, linking it as `[stuff from a](./a.md)` eliminates the error.
* Links with / don't exist, browser has a workaround, crawler does not.
Checked with curl.
* `cmd/docs/generate-cli-docs.go` generates invalid links between root
and sub command. Apparently only if folder name equals root cmd name.
Corentin Néau