Merge pull request #58 from ruslo/fix.include

Fix missing public include directory
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d0780c4..a32cb00 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -411,6 +411,7 @@
 target_include_directories (glog BEFORE PUBLIC
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>"
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>"
+  "$<INSTALL_INTERFACE:include>"
   PRIVATE ${CMAKE_CURRENT_BINARY_DIR}
   PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)