[doc][develop] Improve docker information

Update the docker image versions.
Add notice for newer version check.

doc/develop.rst

@@ -35,7 +35,7 @@ Go through the following sequence of commands:
    $ #install miniconda (version 4.4 or above required)
    $ conda activate base
    $ cd beat.backend.python #cd into this package's sources
-   $ ../bob.admin/conda/conda-bootstrap.py --overwrite --python=2.7 beat-core-dev
+   $ ../bob.admin/conda/conda-bootstrap.py --overwrite --python=3.6 beat-core-dev
    $ conda activate beat-core-dev
    $ #n.b.: docker must be installed on your system (see next section)
    $ buildout -c develop.cfg
@@ -68,17 +68,23 @@ execute algorithms or experiments.
 We use specific docker images to run user algorithms. Download the following
 base images before you try to run tests or experiments on your computer::
 
-  $ docker pull docker.idiap.ch/beat/beat.env.system.python:1.1.2
-  $ docker pull docker.idiap.ch/beat/beat.env.db.examples:1.1.1
-  $ docker pull docker.idiap.ch/beat/beat.env.client:1.2.0
-  $ docker pull docker.idiap.ch/beat/beat.env.cxx:1.0.2
+  $ docker pull docker.idiap.ch/beat/beat.env.system.python:1.3.0
+  $ docker pull docker.idiap.ch/beat/beat.env.db.examples:1.4.0
+  $ docker pull docker.idiap.ch/beat/beat.env.client:2.0.0
+  $ docker pull docker.idiap.ch/beat/beat.env.cxx:2.0.0
 
 Optionally, also download the following images to be able to re-run experiments
-downloaded from the BEAT platform (not required for unit testing). These docker images corresponds to the python environment available on the platform. Keep in mind that at the moment you cannot use different environment to run each block when you are using BEAT locally::
+downloaded from the BEAT platform (not required for unit testing). These docker
+images corresponds to the python environment available on the platform. Keep in
+mind that at the moment you cannot use different environments to run each block
+when you are using BEAT locally (meaning not using the Docker executor)::
 
-  $ docker pull docker.idiap.ch/beat/beat.env.python:0.0.4
-  $ docker pull docker.idiap.ch/beat/beat.env.python:1.0.0
-  $ docker pull docker.idiap.ch/beat/beat.env.db:1.2.2
+  $ docker pull docker.idiap.ch/beat/beat.env.python:1.1.0
+  $ docker pull docker.idiap.ch/beat/beat.env.python:2.0.0
+  $ docker pull docker.idiap.ch/beat/beat.env.db:1.4.0
+
+Before pulling these images, you should check the registry as there might have
+been new release (i.e. rX versions).
 
 To run an experiment using docker you should specify the docker image when defining the experiment, then use the `--docker` flag when using `beat.cmdline`::