Add project files.

.github/workflows/dotnet.yml

@@ -0,0 +1,26 @@
+name: .NET
+
+on:
+    push:
+        branches: [master]
+    pull_request:
+        branches: [master]
+
+jobs:
+    build:
+        runs-on: ${{ matrix.os }}
+        strategy:
+            matrix:
+                dotnet: ["3.1.404", "5.0.101"]
+                os: [ubuntu-latest, windows-latest, macOS-latest]
+
+        steps:
+            - uses: actions/checkout@v2
+            - name: Setup .NET
+              uses: actions/setup-dotnet@v1
+              with:
+                  dotnet-version: ${{ matrix.dotnet }}
+            - name: Install dependencies
+              run: dotnet restore
+            - name: Build
+              run: dotnet build --configuration Release --no-restore