add missing packages

rhel8/index.md

@@ -40,7 +40,7 @@ is hanging. Usually it is after the installation of `/etc/sssd/sssd.conf`. Just
 | RHEL 7 | RHEL 8 | remarks |
 | ---    | ---    | ---     |
 | `a2ps`   | recommends to use `enscript` instead | [`enscript` upstream](https://www.gnu.org/software/enscript/) [`a2ps` upstream](https://www.gnu.org/software/a2ps/)   |
-| blt | - | [`blt` upstream](http://blt.sourceforge.net/) |
+| blt | - | [`blt` upstream](http://blt.sourceforge.net/), does not work with newer Tk version ([source](https://wiki.tcl-lang.org/page/BLT)) |
 | ... | ... | here I stopped research, please report/document further packages |
 | `devtoolset*` | `gcc-toolset*` | |