Document why we compile Google Test ourselves.

CMakeLists.txt

@@ -3,6 +3,10 @@ project(FORMAT)
 
 add_library(format format.cc)
 
+# We compile Google Test ourselves instead of using pre-compiled libraries.
+# See the Google Test FAQ "Why is it not recommended to install a
+# pre-compiled copy of Google Test (for example, into /usr/local)?"
+# at http://code.google.com/p/googletest/wiki/FAQ for more details.
 if (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/gtest/CMakeLists.txt)
   add_subdirectory(gtest)
   include_directories(gtest/include)