Update Readme

[lxbarth]

Is this project current at all in the light of openstreetmap-carto deployed on osm.org?

• README needs to reflect the legacy status of this project
• README should reference successor: Update Readme gravitystorm/openstreetmap-carto#135

[gravitystorm]

This is actually a mirror of the repository at https://trac.openstreetmap.org/browser/subversion/applications/rendering/mapnik/

I don't know if anyone who commits to svn follows the issues here on github though.

[gravitystorm]

At the very least, we should update the repo description. "Mirror of the mapnik stylesheets used on OpenStreetMap.org" is misleading, since the stylesheets aren't used on osm.org any more.

[gravitystorm]

This is now fixed - both the repo description and README have been updated (thanks to @tomhughes and @harry-wood .

(But I can't close the issue)