Clearly state that GeoJSON is a RFC6906 profile of JSON.

RFC4267 doesn't specify any media type parameters, but a profile
parameter is a big help to GeoJSON. Without it, we'd probably need
a custom media type. GeoJSON's use of a profile parameter does not
alter the (JSON) processing model, it only indicates that the root
object contains geographic features to be interpreted according to
the GeoJSON spec.
Merge branch 'master' of github.com:GeoJSONWG/draft-geojson
More narrative introduction.
Merge pull request #13 from sgillies/intro-narrative

Reworking the introduction