ENH: new readme with docker instructions.

README.md

-# MoringaV2
+# The Moringa Land Cover Toolbox
+## Installation via Docker
 
-New version of the Moringa Land Cover processing chain.
\ No newline at end of file
+### Install Docker
+*Windows 10+*  
+```
+Install Docker Desktop then use the command prompt (cmd.exe) to execute docker pull and docker create.
+```
+
+*Debian and Ubuntu*  
+See full documentation here : https://docs.docker.com/engine/install/ubuntu/
+
+### Use docker to pull, create, exec...
+
+```bash
+# Pull image (default tag is "latest")
+docker pull gitlab-registry.irstea.fr/raffaele.gaetano/moringav2
+
+# Create a persistent, interactive (named "moringa") container with 
+# a volume attached, here with home dir, but it can be any directory. 
+# Beware of ownership issues, see the last section of this doc.
+docker create --interactive --tty --volume /home/$USER:/home/ubuntu/data \
+    --name moringa gitlab-registry.irstea.fr/raffaele.gaetano/moringav2 /bin/bash
+
+# Start the container in interactive mode (brings up a bash shell)
+docker start -i moringa
+
+# Start the container in background mode
+docker start moringa
+
+# Execute a command in the container while in background mode
+docker exec moringa ls -alh
+
+# Stop a container (do this always when you're done!)
+docker stop moringa
+
+# Remove a persistent container
+docker rm moringa
+```
+
+### Fix volume ownership issue (required if host's UID > 1000)
+When mounting a volume, you may experience errors while trying to write files from within the container.  
+Since the default user (ubuntu) is UID 1000, you won't be able to write files into your volume  
+which is mounted with the same UID than your linux host user (may be UID 1001 or more).  
+In order to address this, you need to edit the container's user UID and GID to match the right numerical value.
+This will only persist in a named container, it is required every time you're creating a new one.
+
+```bash
+# Create a named container (here with your HOME as volume), 
+# Docker will automatically pull the image.
+docker create --interactive --tty --volume /home/$USER:/home/ubuntu/data \
+    --name moringa gitlab-registry.irstea.fr/raffaele.gaetano/moringav2 /bin/bash
+    
+# Start a background container process (in order to exec root commands, 
+# because default user isn't sudoer)
+docker start moringa
+
+# Exec required commands with user root (here with host's ID, 
+# replace $UID and $GID with desired values)
+docker exec --user root moringa usermod ubuntu -u $UID
+docker exec --user root moringa groupmod ubuntu -g $GID
+
+# Force reset ownership with updated UID and GID. Make sure to double check that.
+docker exec moringa id
+
+# Recursive chown will apply to your volume in /home/ubuntu/data
+# ATTENTION: ownership is affected also outside the docker. 
+# Beware of folders shared with other users.
+docker exec --user root moringa chown -R ubuntu:ubuntu /home/ubuntu
+
+# Stop the background container and start a new interactive shell, you're done!
+docker stop moringa
+docker start -i moringa
+```