Update LICENSE, README.md files

LICENSE

+MIT License
+
+Copyright (c) 2019 Christian Blechert
+
+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

+The base image for all brickburg container images.
+
+## Build a rootfs
+
+Building a rootfs requires root privileges on the system.
+So we create a rootfs tarball manually, host the tarball
+on a webserver and fetch it on each image build.
+
+At the build the bootstrapper script runs a full system upgrade.
+So there is no need to recreate the rootfs tarball on each container build.
+
+### Usage
+
+```sh
+./build-rootfs.sh --debianrelease stretch --output ~/Downloads/rootfs-stretch.tar.gz
+```
+
+## Build the container
+
+The build script extracts the rootfs tarball into an empty container image
+and executes the bootstrapper script. The script configures the image with proper
+debian apt sources and disables many stuff that is not needed in an docker image.
+
+Also it performs an final cleanup which removes all packages that are not required
+to run the packages which are listed on the `keeppkg.txt` text file.
+
+At the end the the image will be flattened.
+
+### Usage
+
+```sh
+./build.sh --rootfstarfile rootfs.tar.gz --imagename brickburg-stretchbase:latest
+```