Add GitHub workflow configurations

.github/workflows/build.yml

@@ -0,0 +1,24 @@
+name: Build CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+    - name: Install dependencies
+      run: sudo apt-get install gcc-riscv64-unknown-elf
+    - name: Make
+      run: make CROSS_PREFIX=gcc-riscv64-unknown-elf-
+    - name: Upload artifacts
+      uses: actions/upload-artifact@v3
+      with:
+        name: kernel.elf
+        path: build/kernel.elf