fix: install yapp preprocessor (#55)

Author: sarahschwartz

.github/workflows/ci-docs.yaml

@@ -54,6 +54,9 @@ jobs:
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@1780873c7b576612439a134613cc4cc74ce5538c # v1.15.2
 
+      - name: Install mdbook-yapp
+        run: cargo install mdbook-yapp --locked
+
       - name: Deploy mdBook to gh-pages
         uses: matter-labs/deploy-mdbooks@c72ae3825faeb7d20cbf3e67714f7253dd0ee7cb
         with: