add info to README and create conda environment file

README.md

-# User guide
+## NEMO User guide
+
 This project contains the source files (rst format) allowing to build the [html files for NEMO User's guide](https://sites.nemo-ocean.io/user-guide/)
 
 If you want to make some changes and updates, you can edit the rst source files in this directory.
 
 The User guide is web-based and is automatically generated from rst files, [namelists and gallery](https://forge.nemo-ocean.eu/nemo/doc). 
 
-Once the changes committed in these 3 projects, one needs to update their links into the project at the top of it [https://forge.nemo-ocean.eu/sites/user-guide](https://forge.nemo-ocean.eu/sites/user-guide), which in turn will trigger the Continuous Integration rebuilding the html files. 
+
+## Cloning with submodules
+
+This repository uses the `namelists` and `gallery` documentation projects as git `submodules`.
+
+So when cloning this repository it is necessary to clone also the related submodules, using the following command
+
+`git clone --recurse-submodules <reponame>`
+
+If the repository was cloned in a standard way, it is possible to checkout submodules using
+
+`git submodule update --init `
+
+
+## Update the online documentation
+
+Once that requested changes are committed to one or all these 3 projects, it is necessary to update their links into this project which in turn will trigger the Continuous Integration rebuilding the html files. 
+
 [This project at the top](https://forge.nemo-ocean.eu/sites/user-guide) is for now available to NEMO Officers only, so that you need to contact your NEMO  Officer to [finalise the update and rebuild the html files](https://forge.nemo-ocean.eu/sites/user-guide/-/blob/main/README.md)
 

environment.yml

+---
+name: nemo-user-guide
+channels:
+  - conda-forge
+
+dependencies:
+  # Multi language support:
+  - python>=3.8
+  - sphinx
+  - sphinxcontrib-bibtex 
+  - sphinx_rtd_theme
+  - pip
+  # regular pip packages
+  - pip:
+    - sphinxext-remoteliteralinclude