Fix spdlog include.

Engine/Source/ThirdParty/spdlog/INSTALL

@@ -0,0 +1,27 @@
+Header Only Version
+==================================================================
+Just copy the files to your build tree and use a C++11 compiler.  
+Or use CMake:
+``` 
+  add_executable(example_header_only example.cpp)
+  target_link_libraries(example_header_only spdlog::spdlog_header_only)
+```
+
+Compiled Library Version
+==================================================================
+CMake:
+```  
+  add_executable(example example.cpp)
+  target_link_libraries(example spdlog::spdlog)
+```
+
+Or copy files src/*.cpp to your build tree and pass the -DSPDLOG_COMPILED_LIB to the compiler.
+
+Important Information for Compilation:
+==================================================================
+* If you encounter compilation errors with gcc 4.8.x, please note that gcc 4.8.x does not fully support C++11. In such cases, consider upgrading your compiler or using a different version that fully supports C++11 standards
+
+Tested on:  
+gcc 4.8.1 and above
+clang 3.5
+Visual Studio 2013