OS X still works with pthread fix - added explanation

common/CMakeLists.txt

@@ -48,6 +48,7 @@ INCLUDE_DIRECTORIES(${PROTOBUF_INCLUDE_DIR})
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_BINARY_DIR})
 
 add_library(cockatrice_common ${common_SOURCES} ${common_HEADERS_MOC})
+# Without this check, Linux will put -pthread out of order in link.txt and build will fail
 if (UNIX)
     target_link_libraries(cockatrice_common cockatrice_protocol pthread)
 else (UNIX)