adds new developer tip for weight file IO

doc/src/dev_info.dox

@@ -38,4 +38,14 @@ Last but not least, a new tests needs to be provided to check for the correctnes
     YAC
   - \code DEBUG_TAGS \endcode all tag strings and their associated tags will be
     printed
+
+\section dev_tips_perf Performance tips
+
+\subsection dev_tips_perf_io IO
+
+- Reading (see interpolation method file \ref interpolation_method_file.h) and
+  writing of weight files is done in parallel by a subset of processes. Which
+  processes access the weight file is determined by the routine
+  \ref compute_io_proc_step. In case of performance issues related to the number
+  of IO processes you should have a look at this routine.
  */