fix tmux docs

docs.it4i/general/accessing-the-clusters/tmux.md

@@ -7,16 +7,28 @@ Tmux is installed on Karolina's login nodes.
 Note that [GNU Screen][2] is not supported, but if you prefer it, you can install it in your `/home` folder:
 
 ```console
-wget https://ftp.gnu.org/gnu/screen/screen-4.8.0.tar.gz
-tar xf screen-4.8.0.tar.gz && rm screen-4.8.0.tar.gz
-cd screen-4.8.0
+#!/bin/bash
+
+# download source code
+wget https://ftp.gnu.org/gnu/screen/screen-4.9.0.tar.gz
+tar xf screen-4.9.0.tar.gz && rm screen-4.9.0.tar.gz
+cd screen-4.9.0
+
+# install screen
+./autogen.sh
 ./configure --prefix=$HOME/.local/screen
 make
 make install
+
+# copy over default etc
 mkdir $HOME/.local/screen/etc
 cp etc/etcscreenrc $HOME/.local/screen/etc/screenrc
-echo "export PATH=$HOME/.local/screen/bin:$PATH" >> $HOME/.bashrc
-cd ../ && rm -rf screen-4.8.0
+
+# set up path
+echo "export PATH=\$HOME/.local/screen/bin:\$PATH" >> $HOME/.bashrc
+
+# clean up
+cd ../ && rm -rf screen-4.9.0
 ```
 
 [1]: https://github.com/tmux/tmux/wiki