Add CI main.

.github/workflows/main.yaml

@@ -0,0 +1,17 @@
+name: GitHub Actions Demo
+run-name: ${{ github.actor }} is testing out GitHub Actions 🚀
+on: [push]
+jobs:
+  Test:
+    runs-on: ubuntu-latest
+    permissions: write-all
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run a multi-line script
+        run: |
+          mkdir build
+          cd build
+          cmake ..
+          make test_qr_decomposition
+          ./test_qr_decomposition
+