README: Update copyright statement slightly

Just changes "Tildes" to "Tildes contributors" and adds an email
address, as recommended.

README.md

@@ -16,10 +16,10 @@ Please see [the Contributing doc](CONTRIBUTING.md) for more detailed information
 
 ## License
 
-Copyright (C) 2018 Tildes
+Copyright (c) 2018 Tildes contributors <code@tildes.net>
 
 This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
 
 This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.
 
-You should have received a copy of the GNU Affero General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
+You should have received a copy of the GNU Affero General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.