Re-organize and improve help command and help info for each command

libexec/tmuxifier-list-sessions

@@ -2,6 +2,16 @@
 set -e
 [ -n "$TMUXIFIER_DEBUG" ] && set -x
 
+# Provide tmuxifier help
+if [ "$1" == "--help" ]; then
+  echo "usage: tmuxifier list-sessions
+
+Aliases: list-ses, lss
+
+List all session layouts."
+  exit
+fi
+
 list=$(find -L "$TMUXIFIER_LAYOUT_PATH" -name "*.session.sh")
 for file in $list; do
   file=${file/$TMUXIFIER_LAYOUT_PATH\//}