[render-blocking] The links of "render-blocking" in fetch are vague

[cathiechen]

What is the issue with the Fetch Standard?

I found the links of "render-blocking" in fetch are vague when walking through the spec.

1. It shows "Possible linking syntaxes", when clicking https://fetch.spec.whatwg.org/#request-render-blocking
2. The value of "render-blocking" of "fetch timing info" is not used anywhere. https://fetch.spec.whatwg.org/#fetch-timing-info-render-blocking Should we make it clear? @xiaochengh @emilio