add (overwrite with) mypy stubs, if available

LICENSE

@@ -1,3 +1,7 @@
+typeshed is licensed under the terms of the Apache license, reproduced below.
+
+= = = = =
+
 Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/
@@ -200,3 +204,34 @@ Apache License
    See the License for the specific language governing permissions and
    limitations under the License.
 
+= = = = =
+
+Parts of typeshed are licensed under different licenses (like the MIT
+License), reproduced below.
+
+= = = = =
+
+The MIT License
+
+Copyright (c) 2015 Jukka Lehtosalo and contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+
+= = = = =
+