Setting up a ClojureScript development environment - Visual Studio Code

I am trying to lower the thresholds of setting up a Clojurescript development environment with an extension to VS Code I call [Calva](https://marketplace.visualstudio.com/items?itemName=cospaia.clojure4vscode). I could write a first version of an Appendix B section about Calva, if you like. It's pretty easy with Calva, since it is mainly about installing the extension and, in case of `shadow-cljs` include a dependency on `cider/nrepl`. Similar to this: https://shadow-cljs.github.io/docs/UsersGuide.html#_calva_vs_code

Let me know if you want me to issue a PR.

Start by reviewing the book's Appendix B and the linked shadow-cljs Calva documentation. Add a Calva section covering extension installation and the cider/nrepl dependency for shadow-cljs, then verify that the setup steps are clear for a ClojureScript development environment.

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