Minor addition about headers

docs/driver.makefile.md

@@ -216,7 +216,12 @@ Having done this, the build/install process runs as follows.
    which says that any target within the directory `$(INSTALL_INCLUDE)` has the target as a dependency i.e.
    `$(INSTALL_INCLUDE)/header.h` depends on `header.h`
 4. Finally, the `vpath` line above tells `make` where to search for that file, and then the instructions tell `make`
-   to run the program defined by `$(INSTALL)` to install the file in the target location.
+   to run the program defined by `$(INSTALL)` to install the file in the target location. Note however that there is
+   one potential source of problems here: the dependency is just the filename alone, and so if you have the following
+   two header files you would like to include: `dir1/header.h` `dir2/header.h` i.e. the same filename, but different
+   locations, then only one of these two will be installed.
+
+   We have implemented a mechanism to get around this, please see the release notes for require 3.3.0.
 
 ### Compiling a .c file