Add <nav> element (#1418)

Author: petele

features/draft/html-elements/nav.yml

@@ -0,0 +1,6 @@
+name: <nav>
+description: The `<nav>` element represents a section of a page whose purpose is to provide navigation links, either within the current document or to other documents.
+spec: https://html.spec.whatwg.org/multipage/sections.html#the-nav-element
+group: html-elements
+compat_features:
+  - html.elements.nav