Update doc

Fix #6

Readme.md

-# Web services based on Python scripts
+# Unl2rdf web demo
 
-Initially deveopped to deploy a serialization converter from the official UNL format to the proposed RDF-UNL format.
+This is a [dockerized](https://www.docker.com/) webdemo of the [unl2rdf java parser](https://gitlab.tetras-libre.fr/unl/unl2rdf)
 
-## How to use
+## Requirements
+
++ [Docker](https://docs.docker.com/get-docker/)
++ [Docker-compose](https://docs.docker.com/compose/install/)
+
+## Install
 
 ```bash
 cp .env.sample .env
 docker-compose up
 ```
 
+The first time this process will take a while as it has to [build](#build-process) the docker images and the [java parser](https://gitlab.tetras-libre.fr/unl/unl2rdf).
+
 Then open in a browser `http://localhost:5000`
 
+## build process
+
+The docker build process consists in three steps
+
+1. On create a debian base image with jdk
+2. Create a build image that retrieve the unl2rdf parser sources and builds it
+3. Create an image to run the flask application
+
+### Triggering a rebuild
+
+Docker caches every step of the build, if the java parser has changed, `docker-compose build` will not detect it, so you have to change `GIT_REF=` in the `.env` file to point to the desired commit, branch or tag. Then you can run `docker-compose build` and only the required steps to rebuild the java parser will run again.
+
 ## Developpement
 
-This is a one page [flask](https://flask.palletsprojects.com) app to convert unl to rdf, the web app is full python, everything is in the file `src/app/app.py`.
+This is a one page [flask](https://flask.palletsprojects.com) app to acces the [unl2rdf parser](https://gitlab.tetras-libre.fr/unl/unl2rdf), the web app is full python, everything is in the file `src/app/app.py` and in `src/app/static/<css|js>`
 
 The display rendering uses the templates in the directory `src/app/templates` see [flakes templating](https://flask.palletsprojects.com/en/1.1.x/quickstart/#rendering-templates).
+
+Js and css dependencies are installed via npm in directory `src/app/static`