Add temp myget nuget package source

This will let package restore work with temp myget package source I have set
up to host the native binaries package.

Author: bording

.nuget/nuget.config

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <add key="Temp MyGet Feed" value="https://www.myget.org/F/bording-libgit2/" />
+  </packageSources>
+</configuration>