Readme 'feature' links incorrect

[bkardell]

See: https://github.com/web-platform-tests/wpt.fyi/blob/main/api/query/README.md#feature

feature query atoms perform a search for tests that have a matching feature label, regardless of browsers.

{"feature": [web-feature-name]}
Where web-feature-name is a string, case-insensitive and matches the filename base for any of the .yml files in the feature-group-definitions directory.

E.g.

Search the nesting feature:

feature:nesting

In both cases the relevant links are 404..