message: clarify why its always safe to not append at end while parsing
diff: @@ -27,6 +27,9 @@ function parseAtRoomMentions(text, partCreator) {
  if (textPart.length) {
  parts.push(partCreator.plain(textPart));
  }
  + // it's safe to never append @room after the last text
  + // as split will report an empty string at the end if
  + // `text` ended in @room.
  const isLast = i === arr.length - 1;
  if (!isLast) {
  parts.push(partCreator.atRoomPill(ATROOM));
  