Add readme text about scope

See #27
Merge pull request #34 from osmlab/readme_osm

Add readme text about scope
add imagery of South Tyrol provicial administration

* WMTS_OF2011_APB-PAB - aerial imagery from 2011, approx. 50cm
  resolution (not as good as bing, but much less distorted in the
  mountains)
* WMTS_TOPOMAP_APB-PAB - a detailed topographical map with contour
  lines, hiking paths, buildings, landuse, etc.

There is an explicit permission [1] for the „production of Open Data derived products”.

Read more:
https://wiki.openstreetmap.org/wiki/AltoAdige_-_Südtirol#Provincia_Autonoma_di_Bolzano_-_Autonome_Provinz_Bozen

[1] (http://sdi.provincia.bz.it/geoserver/ows?service=wms&version=1.3.0&request=GetCapabilities)
Merge pull request #36 from tyrasd/prov-bz

add imagery by South Tyrol's provicial administration
added Erlangen Luftbild
Add license_url to schema
Merge pull request #38 from hno2/gh-pages

added Erlangen Luftbild
Add license URL