Polish README and error messages, add a rofi wrapper script

ptgdp-rofi

@@ -0,0 +1,32 @@
+#! /bin/bash
+#
+# ptgdp-rofi
+# Uses rofi to select a ptgdp playlist in ~/Music/Playlists
+# Copyright (C) 2019 Vintage Salt <rehashedsalt@cock.li>
+#
+# Distributed under terms of the MIT license.
+#
+set -e
+
+_xdguserdirs="${XDG_CONFIG_HOME:-$HOME/.config}/user-dirs.dirs"
+[ -z "$XDG_MUSIC_DIR" ] && [ -r "$_xdguserdirs" ] && source "$_xdguserdirs"
+unset _xdguserdirs
+playlistdir="${XDG_MUSIC_DIR:-$HOME/Music}/Playlists"
+
+files=$(find "$playlistdir" -type f -name \*.gdp)
+if [ -n "$files" ]; then
+	playlists=""
+	while read file; do
+		filebase="$(basename -- "$file")"
+		filebase="${filebase%.gdp}"
+		[ -n "$playlists" ] && playlists+=$'\n'
+		playlists+="$filebase"
+	done <<< "$files"
+else
+	echo "No playlists found"
+	exit 1
+fi
+prompt="ptgdp"
+choice="$(rofi -dmenu -i -p "$prompt" <<< "$playlists" 2>/dev/null)"
+[ -z "$choice" ] && exit 2
+exec ptgdp -p "$playlistdir"/"$choice".gdp