move the space requirements into single place, README.core

libisoburn/trunk/releng/run_all_releng

@@ -91,10 +91,7 @@ ${SELF} runs executables from CWD starting
 with releng_*, passing them its own options.
 stdout/stderr output stored in:
  ${CLOG}
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-self-generated data are stored in ${GEN_DATA_DIR}.
-required space for these data is about 300 megabytes.
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 examples:
 # run xorriso and keep the self-generated data
  $ ./${SELF} -x path/to/xorriso [-k]