add a LICENSE file containing the MIT license text, as is necessary

As far as I can discern Paul's intent is that all of this code is licensed as MIT, but that license requires a copy of the license text to be provided with the source. As ogr2osm-translations can be cloned separately from ogr2osm, it's probably a good idea to have a copy of LICENSE here. I checked the commit history of each translation file and AFAICS only Paul has contributed, so the attribution should be correct (assuming my Vancouver translation is accepted).