docs: add BSD licence and enhance README

LICENCE

@@ -0,0 +1,56 @@
+Copyright © 2017, Michael Stapelberg and contributors
+Copyright © 2021, guardianproject
+Copyright © 2025-2026, SR2 Communications Limited
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * 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.
+
+    * Neither the name of Michael Stapelberg nor the
+      names of contributors may be used to endorse or promote products
+      derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY Michael Stapelberg ''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 Michael Stapelberg 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.
+
+Additionally, we include here the original licence terms as required by the terms
+of the Butter Box for Raspberry Pi project, which apply only to the code derived
+from that project:
+
+MIT License
+
+Copyright (c) 2021 guardianproject
+
+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.
+

README.md

@@ -1,5 +1,28 @@
-# Churn
+# Butter Churn
 
-This is work in progress. 
+[![License](https://img.shields.io/badge/License-BSD_3--Clause-orange.svg)](https://opensource.org/licenses/BSD-3-Clause)
 
-To build a butter image, run vmdb2 --rootfs-tarball=my_image.tar.gz --output my_image.img --log my_image.log
+Tool for building Butter Box disk images.
+
+## Usage
+
+To build a butter image, run:
+
+```sh
+vmdb2 --rootfs-tarball=my_image.tar.gz --output my_image.img --log my_image.log
+```
+
+## Copyright and Licence
+
+© 2017, Michael Stapelberg and contributors
+© 2021 guardianproject
+© SR2 Communications Limited
+
+See [LICENCE](./LICENCE) for details of the BSD-3 clause licence.
+
+This project is a derivative work of:
+
+* [Butter Box for Raspberry Pi](https://gitlab.com/likebutter/butterbox-rpi)
+  licensed under the MIT licence.
+* [Raspberry Pi Image Specs](https://salsa.debian.org/raspi-team/image-specs)
+  licensed under the 3-clause BSD licence.