add bash completion support

This fixes #188.

bash-completion/openrc

@@ -0,0 +1,24 @@
+# Copyright (c) 2017 The OpenRC Authors.
+# See the Authors file at the top-level directory of this distribution and
+# https://github.com/OpenRC/openrc/blob/master/AUTHORS
+#
+# This file is part of OpenRC. It is subject to the license terms in
+# the LICENSE file found in the top-level directory of this
+# distribution and at https://github.com/OpenRC/openrc/blob/master/LICENSE
+# This file may not be copied, modified, propagated, or distributed
+# except according to the terms contained in the LICENSE file.
+
+#
+# openrc completion command
+#
+_openrc()
+{
+	local cur
+	COMPREPLY=()
+	cur="${COMP_WORDS[COMP_CWORD]}"
+	if [[ ${#COMP_WORDS[*]} -le 2 ]]; then
+		COMPREPLY=($(compgen -W "$(rc-status --list)" -- $cur))
+	fi
+	return 0
+} &&
+complete -F _openrc openrc