[DOCS] - Update jekyll Docker image to jekyll/jekyll:4.2.2 in README

[DhavalGojiya]

📌 Fixes #48

This PR updates the Docker command in the README.md to use a newer Jekyll image:

-     -it jekyll/jekyll:3.8 \
+     -it jekyll/jekyll:4.2.2 \

---

We may also need to update build.sh line 337:

- docker run --rm --volume="$PWD:/srv/jekyll" -it jekyll/builder:3.8 jekyll build
+ docker run --rm --volume="$PWD:/srv/jekyll" -it jekyll/builder:4.2.2 jekyll build

Should we upgrade the jekyll/builder version here as well, to stay consistent with the rest of the setup?