Add CI job to verify that we have no broken links. (#50)

Fix all broken links.

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: "CI"
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  check-links:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Build book
+        run: |
+          cd book
+          curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.40/mdbook-v0.4.40-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=.
+          ./mdbook build
+      - name: Link Checker
+        uses: lycheeverse/lychee-action@v1
+        with:
+          fail: true
+          args: |
+            --exclude-loopback 
+            --require-https 
+            --no-progress 
+            book/book