Fix explanation of config.h generation in bare config.h.

Change-Id: I66488dc09670c4b178db7a3ae21b93fcc84ca051

config/ceres/internal/config.h

@@ -32,10 +32,11 @@
 //
 // IMPORTANT: Most users of Ceres will not use this file, when compiling Ceres
 //            with CMake, CMake will configure a new config.h with the currently
-//            selected Ceres compile options and copy it into the source
-//            directory before compilation.  However, for some users of Ceres
-//            who compile without CMake, this file ensures that Ceres will
-//            compile, with the user either specifying manually the Ceres
+//            selected Ceres compile options in <BUILD_DIR>/config, which will
+//            be added to the include path for compilation, and installed with
+//            with the public Ceres headers.  However, for some users of Ceres
+//            who compile without CMake (Android), this file ensures that Ceres
+//            will compile, with the user either specifying manually the Ceres
 //            compile options, or passing them directly through the compiler.
 
 #ifndef CERES_PUBLIC_INTERNAL_CONFIG_H_