Add badges to Cargo.toml

Cargo.toml

 keywords = ["openstreetmap", "osm", "pbf", "protocolbuffer", "protobuf"]
 license = "MIT/Apache-2.0"
 
+[badges]
+travis-ci = { repository = "b-r-u/osmpbf" }
+appveyor = { repository = "b-r-u/osmpbf" }
+
 [features]
 default = ["system-libz"]
 system-libz = ["flate2"]