Add more context to Docker config

.devcontainer/devcontainer.json

@@ -1,11 +1,22 @@
 {
  "name": "LaTeX",
- // Either build the local Dockerfile directly (which can take hours due to slow
- // TeXLive servers):
+ // Instead of *building* the accompanying Dockerfile and its whole context, like:
+ //
  // "build": {
  // "dockerfile": "image/Dockerfile",
  // },
- // or rather use a pre-existing image and simply download from DockerHub:
+ //
+ // simply download the prepared image the author has already uploaded, based on
+ // what's found inside the `image/` directory.
+ // Advantages:
+ // - build process is slow (downloads from TeX servers), each user doing it every
+ // time is too much. It can take *hours* in worst-cases
+ // - build might fail for various reasons
+ // It is much easier to download the ready-made image.
+ // Disadvantages:
+ // - cannot easily iterate on the Docker image, need to go through Docker Hub.
+ // Recourse: simply change the below to use the *local image temporarily*
+ // - Upstream image on Docker Hub might not be the latest
  "image": "alexpovel/latex",
  // Set *default* container specific settings.json values on container create.
  "settings": {