README: change guidance and demphasise v1

* Recommend that normalize.css is used as library code (i.e., not
  modified).

* Add a note that v1 is no longer actively developed.
Add Component(1) install instructions
Fix incorrect closing tag in `test.html`
Add IE 10 to checkbox/radio normalization comments
Fix component.json

The Component(1) spec was updated to require a `repo` property.
Update CHANGELOG
v2.1.3