Clarifying how to install for gRPC C++

INSTALL.md

@@ -3,7 +3,7 @@
 For language-specific installation instructions for gRPC runtime, please
 refer to these documents
 
- * [C++](examples/cpp)
+ * [C++](examples/cpp): Currently to install gRPC for C++, you need to build from source as described below.
  * [C#](src/csharp): NuGet package `Grpc`
  * [Go](https://github.com/grpc/grpc-go): `go get google.golang.org/grpc`
  * [Java](https://github.com/grpc/grpc-java)

examples/cpp/README.md

@@ -2,7 +2,7 @@
 
 ## Installation
 
-To install gRPC on your system, follow the instructions [here](../../INSTALL.md).
+To install gRPC on your system, follow the instructions to build from source [here](../../INSTALL.md). This also installs the protocol buffer compiler `protoc` (if you don't have it already), and the C++ gRPC plugin for `protoc`.
 
 ## Hello C++ gRPC!