[DOC] Make the document more clear.

Author: Alex Chi

README.md

@@ -7,7 +7,7 @@ Link the google's `protocol bufffers` library as the third party in [Unreal Engi
 Usage
 -----
 
-1. Import or copy this project into `<your project>/Source/ThirdParty/libprotobuf`.
+1. Import or copy this project into `<your project or plugin>/Source/ThirdParty/libprotobuf`.
 1. Add the libprotobuf as a module into `<your project>.Build.cs`
   * `PrivateDependencyModuleNames.AddRange(new string[] { "CoreUObject", "Engine", "libprotobuf" });`
 1. Generate two code files (header & source, ex: Message.pb.h & Message.pb.cc) of the protocal by `protoc` for `cpp`. (Ref: [Google's Protocol Buffers][])