doc: Add website deployment documentation (#3889)

Author: slarse

doc/_release/WEBSITE.md

@@ -0,0 +1,36 @@
+# Spoon website documentation for maintainers
+
+This document contains everything you need to know about the Spoon website in order to maintain and update it. The website is currently hosted at https://spoon.gforge.inria.fr/.
+
+## Building the website locally
+
+To build the website locally, you only need to have Jekyll installed, which is a [Ruby gem](https://en.wikipedia.org/wiki/RubyGems). Typically, you would install this with the `gem` command, assuming that you have Ruby (2.4+ required) installed.
+
+```bash
+$ gem install jekyll
+```
+
+Pay attention to the output of `gem install`, it provides useful information such as warning when the installed `jekyll` binary is not on your `PATH`. When `jekyll` is installed, you can serve the website by going to the `doc` directory and executing `jekyll serve`.
+
+```bash
+$ jekyll serve
+Configuration file: /path/to/spoon/doc/_config.yml
+            Source: /path/to/spoon/doc
+       Destination: /path/to/spoon/doc/_site
+ Incremental build: disabled. Enable with --incremental
+      Generating... 
+                    done in 0.102 seconds.
+ Auto-regeneration: enabled for '/path/to/spoon/doc'
+    Server address: http://127.0.0.1:4000/
+  Server running... press ctrl-c to stop.
+```
+
+The website will automatically regenerate as you make changes in the source files.
+
+> **Note:** You may also need to separately install the gem `webrick` if there is a crash when running `jekyll serve`.
+
+> **Note:** To get the proper index page, copy the root README to `doc/doc_homepage.md`.
+
+## Deploying the website
+
+The website is automatically deployed to the [SpoonLabs GitHub Pages repository](https://github.com/spoonlabs/spoonlabs.github.io). The deployment is handled by a GitHub Actions workflow in said repository, [see the README](https://github.com/SpoonLabs/SpoonLabs.github.io/blob/main/README.md) for details.