Added script description

README.md

@@ -2,3 +2,20 @@
 
 A script to build the mumble-web app in a docker image.
 
+The script will clone the [mumble-web](https://github.com/Johni0702/mumble-web) repository.
+If the repository already was cloned it will pull the latest commits.
+Afterwards the docker image, defined in the [Dockerfile](https://gitlab.cvh-server.de/aco/build-mumble-web/-/blob/master/Dockerfile), will be build.
+
+**Dockerfile**
+
+  - alpine:edge
+  - copy content of repository into image
+  - install git and npm
+  - npm: install, run build, audit fix, audit
+
+The image contains the generated files of the app, which can be published by a webserver.
+To copy these files out of the image it is necessary to create a container out of this image.
+Therefore the command 'docker create' needs to be executed.
+Afterwards the directory can be copied with 'docker cp'.
+
+The container and the image are not longer needed, so they will be removed at the end.
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