Add readme with some documentation.

web/README.md

@@ -0,0 +1,21 @@
+# Instructions to build and deploy the BOPTEST website
+
+## Deploy website locally
+
+### If you have Jekyll
+
+If you already have a Jekyll environment installed and functional you can directly use the command `make build_docs_and_serve_web` to build the docs and test the website in your browser. 
+
+### If you don't have Jekyll
+
+If you don't have Jekyll you can create the Docker environment to build the website with the command `make build-env`. 
+Note that this is the environment used to build and serve the actual website so you this procedure also ensures you're working with the right environment. 
+After the environment is created (only needs to be created once) you can use the command `make run-build-docs-and-serve-web` to build the docs and test the website in your local browser. 
+
+## Deploy the website with GitHub Actions
+
+Normally, GitHub actions uses a default workflow to deploy the website from a branch with the source files living either at the `/` or the `/docs` directory of the repository.
+We use a [custom workflow with GitHub Pages](https://docs.github.com/en/pages/getting-started-with-github-pages/using-custom-workflows-with-github-pages) to benefit from a controlled build environment and the possibility to have the website-related files in a dedicated `/web` directory. The specification of this custom workflow is located at `/.github/workflows/custom-web-build.yml` and it mostly follows the default workflow followed by GitHub Pages but with these two main modifications: 
+
+1. Uses a predefined Docker environment to build the docs-* files and the website content sources.
+2. Serves the website from the `/web` directory (instead of `/docs`).