Added instructions to manually download the dependencies

csharp/.gitignore

@@ -26,6 +26,8 @@ mono/protoc
 build_output
 build_temp
 build/msbuild*.log
+lib/Microsoft.Silverlight.Testing
+lib/NUnit
 
 #
 # 	Untracked files
@@ -38,3 +40,4 @@ mono/TestResult.xml
 mono/.libs
 mono/*.exe
 mono/*.dll
+lib/protoc.exe

csharp/lib/README.md

+This directory used to contain the binary dependencies, but they were removed during a cleanup associated with importing the project
+into google/protobuf repository. Before we figure a better way to manage the dependencies, you will have to manually download the dependencies 
+to be able to build the test projects:
+
+1. Download https://github.com/jskeet/protobuf-csharp-port/archive/2.4.1.555.zip
+2. Open the archive and copy following files into this directory:
+   * `lib/Microsoft.Silverlight.Testing/`
+   * `lib/NUnit/`
+   * `lib/proto.exe`
+
+After that, you should be able to fully build the C# protobufs Visual Studio solutions.
+
+TODO(jtattermusch): the way we pull in dependencies needs to change