Update README.md

README.md

@@ -5,6 +5,30 @@ Forked from [RPi-Distro/pi-gen](https://github.com/RPi-Distro/pi-gen)
 _Tool used to create a custom Raspbian image to use Thymio easily_
 
 
+## Build
+
+To build the custom Raspbian image, first download this repository.
+```bash
+git clone https://gitlab.laas.fr/tpillot/pi-gen-thymio.git
+cd pi-gen-thymio
+```
+Then move and edit the configuration file with your wifi SSID and password.
+```bash
+mv config.example config
+vim config
+```
+
+If you are on either Debian Buster or Ubuntu Xenial, you will need to install the
+[dependencies](#dependencies) below and run `./build.sh`.
+
+On other Linux distribution, you need to install Docker to build the image.
+```bash
+./build-docker.sh
+```
+
+The built image can be found in the `deploy` directory.
+
+
 ## Dependencies
 
 pi-gen runs on Debian based operating systems. Currently it is only supported on