add a simple netcore build for Linux

.github/workflows/netcore.yml

@@ -0,0 +1,17 @@
+name: Build and test with .NET Core
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Setup .NET Core
+      uses: actions/[email protected]
+      with:
+        dotnet-version: 2.2.108
+    - name: Build with dotnet
+      run: ./build.sh --coreonly=false --linksources=true --verbosity=verbose