Add Dockerfile to enable local linux testing on Windows

Author: sblom

Dockerfile

@@ -0,0 +1,20 @@
+# If you want to build and test under Linux using a docker container, here's how:
+#
+#> docker build -t json-ld.net .
+#> docker run --rm json-ld.net dotnet test -v normal
+
+# .NET Core 2.1 on Ubuntu 18.04 LTS
+FROM mcr.microsoft.com/dotnet/core/sdk:2.1-bionic
+
+WORKDIR /App
+
+# First we ONLY copy sln and csproj files so that we don't have to re-cache
+# dotnet restore every time a .cs file changes
+COPY src/json-ld.net/json-ld.net.csproj src/json-ld.net/json-ld.net.csproj
+COPY test/json-ld.net.tests/json-ld.net.tests.csproj test/json-ld.net.tests/json-ld.net.tests.csproj
+COPY JsonLD.sln JsonLD.sln
+RUN dotnet restore
+
+# Then we copy everything and run dotnet build
+COPY . .
+RUN dotnet build