added protoc.exe and well known protobuf files to the nuspec file

csharp/src/Google.Protobuf/Google.Protobuf.nuspec

@@ -11,7 +11,7 @@
     <licenseUrl>https://github.com/google/protobuf/blob/master/LICENSE</licenseUrl>
     <projectUrl>https://github.com/google/protobuf</projectUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <releaseNotes>C# Protocol Buffers</releaseNotes>
+    <releaseNotes>C# proto3 support</releaseNotes>
     <copyright>Copyright 2015, Google Inc.</copyright>
     <tags>Protocol Buffers Binary Serialization Format Google proto proto3</tags>
   </metadata>
@@ -20,5 +20,19 @@
 	<file src="bin/ReleaseSigned/Google.Protobuf.pdb" target="lib/portable-net45+netcore45+wpa81+wp8" />
 	<file src="bin/ReleaseSigned/Google.Protobuf.xml" target="lib/portable-net45+netcore45+wpa81+wp8" />
 	<file src="**\*.cs" target="src" />
+	<file src="..\..\..\cmake\Release\protoc.exe" target="tools" />
+	<file src="..\..\..\src\google\protobuf\any.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\api.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\descriptor.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\duration.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\empty.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\field_mask.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\source_context.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\struct.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\timestamp.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\any.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\type.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\wrappers.proto" target="tools\google\protobuf" />
+	<file src="..\..\..\src\google\protobuf\compiler\plugin.proto" target="tools\google\protobuf\compiler\plugin.proto" />
   </files>
 </package>