Include shell completions in the executable

doc/short-help.txt

@@ -58,6 +58,8 @@ Options:
           Only print the lines from N to M.
   -L, --list-languages
           Display all supported languages.
+      --completion <SHELL>
+          Show shell completion for a certain shell. [possible values: bash, fish, zsh, ps1]
   -h, --help
           Print help (see more with '--help')
   -V, --version