Remark on how to fix exit code 5 of Questasim for unb2b.

doc/erko_howto_tools.txt

@@ -88,6 +88,8 @@ source also radiohdl tools
 
 > run_modelsim unb1 &
 
+Questasim had Exit code 5 = "Cannot create/open/find/read/write a design library"
+during tb simulation load --> fixed by "sudo chmod a+w -R modelsim_altera_libs/18.0".
 
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 * RadioHDL with SVN