use git to get the prelude (#60)

Summary:
Pull Request resolved: #60

since where we are trying to put the prelude directory is already the root of a git repo, `buck2  init --git` is inappropriate. instead ~~use git to get a copy as a submodule~~ delegate to `dtolnay/install-buck2@latest` to pull in  the prelude submodule (at a coherent version with the buck2 installed)

Differential Revision:
D53099111

Privacy Context Container: L1124100

fbshipit-source-id: 383f0ff16741f6bf35f9bc7e8225f85f91095e60

.github/workflows/buck-build-and-test.yml

@@ -15,6 +15,8 @@ jobs:
       - uses: actions/checkout@v4
       - uses: Swatinem/rust-cache@v2
       - uses: dtolnay/install-buck2@latest
+        with:
+          prelude-submodule: prelude
       - run: sudo apt-get update && sudo apt-get install opam
         if: matrix.os == 'ubuntu'
       - run: brew install opam
@@ -25,5 +27,8 @@ jobs:
       - run: ./ocaml-setup.sh
       - run: cargo install --git https://github.com/facebookincubator/reindeer.git reindeer --force
       - run: reindeer --third-party-dir shim/third-party/rust buckify
+      # - run: |-
+      #     git submodule add https://github.com/facebook/buck2-prelude.git prelude
+      #     git submodule update --init --depth 1
       - run: buck2 build shim//third-party/... -v 2
       - run: buck2 build root//... -v 2