fixed typo

doc.zih.tu-dresden.de/docs/software/zsh.md

 # ZSH
 
-The ZSH, short for `z-shell`, is an alternative shell for Linux that offers many convienence features
+The ZSH, short for `z-shell`, is an alternative shell for Linux that offers many convenience features
 for productive use that `bash`, the default shell, does not offer.
 
 This should be a short introduction to `zsh` and offer some examples that are especially useful on Taurus.