Add VitePress instructions to BUILD.md (#2675)

* Update BUILD.md

Update BUILD.md to add information on how to edit/build/preview the docs using the new Markdown version + VitePress

* Updated styling for commands in the BUILD.md new docs sections

* Update BUILD.md

Co-authored-by: Pavan Navarathna <[email protected]>

* Update BUILD.md

Co-authored-by: Pavan Navarathna <[email protected]>

* Reformat to stay under 80 chars per line.

---------

Co-authored-by: Pavan Navarathna <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

BUILD.md

@@ -147,6 +147,37 @@ The `docs` target uses the `ghcr.io/kanisterio/docker-sphinx` public image to
 generate the HTML documents and store them in your local `/docs/_build/html`
 folder.
 
+## New Documentation
+
+We have started experimenting, and will soon fully transition, to using
+ [VitePress](https://vitepress.dev/) to generate Kanister documentation.
+This requires the documentation files to be written in 
+[Markdown](https://www.markdownguide.org/), along with some 
+[extensions](https://vitepress.dev/guide/markdown).
+
+This new documentation system offers a live-dev server that will dynamically
+render Markdown documentation files as you are making changes to them on your
+local machine/branch.
+To start this development server, place yourself in the `new_docs` folder, then
+run the following commands:
+
+```sh
+pnpm install
+pnpm run docs:dev
+```
+
+To render/build the docs locally (it will generate static assets, like HTML
+pages, Javascript/CSS files, etc.), use this command:
+```sh
+pnpm run docs:build
+```
+
+To start a local webserver that you can use to preview the documentation that
+has been rendered by the command above, use this command:
+```sh
+pnpm run docs:preview
+```
+
 ## New Blueprints
 
 If you have new blueprints that you think will benefit the community, feel free