add ZSH completion function _grc

Based on zsh's provided _sudo function

_grc

@@ -0,0 +1,25 @@
+#compdef grc
+
+setopt localoptions extended_glob
+
+local environ e cmd
+local -a args
+local -a _comp_priv_prefix
+
+zstyle -a ":completion:${curcontext}:" environ environ
+
+for e in "${environ[@]}"
+do local -x "$e"
+done
+
+args=(
+  '(-e --stderr)'{-e,--stderr}'[redirect stderr; do not automatically redirect stdout]'
+  '(-s --stdout)'{-s,--stdout}'[redirect stdout; even with -e/--stderr]'
+  '(-c <name>--config=<name>)'{-c+,--config=-}'[use <name> as configuration file for grcat]:file:_files'
+  '--color=-[colo?urize output]:color:(on off auto)'
+  '(-h --help)'{-h,--help}'[display help message and exit]'
+  '--pty[run command in pseudotermnial (experimental)]'
+  '*::arguments:{ _normal }'
+)
+
+_arguments -s $args