Add licence and authors

AUTHORS

+Authors of onion-grab
+
+The copyright on the onion-grab implementation is held by the respective
+authors.
+
+Unless file-specific copyright headers say otherwise, onion-grab is
+permissively licensed according to the BSD 2-Clause License (see the
+LICENSE file).
+
+This file contains only a summary; for more fine-grained information on
+who authored a particular file or feature, please refer to the version
+control history at:
+
+  TODO: add url
+
+File-specific copyright headers should be used when necessary to
+document the origin of a file's contents, e.g., for code copied from
+other sources, or governed by different license requirements.
+
+Authors, in chronological order of initial contribution:
+
+  Rasmus Dahlberg

LICENSE

+BSD 2-Clause License
+
+Copyright (c) 2023, the onion-grab authors
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

@@ -135,3 +135,7 @@ Get in touch if you know a fix, e.g., based on `ulimit` and `sysctl` tinkering.
 ## Contact
 
   - rasmus (at) rgdd (dot) se
+
+## Licence
+
+BSD 2-Clause License