Finding group rooms is difficult

Most of the users coming from commercial platforms doesn't get the tabs at the bottom of the room list.

**To Reproduce**
1. Find a non-techie user
2. Recommend Matrix to them
3. Invite them to a group room (in half of the cases they don't know where to accept)

**Expected behavior**
Easier to find groups.

**Suggestion:**
- If user is in a number of rooms that fits on the screen even without scrolling, then display DMs and groups without differentiating between them, on the same screen (like Messenger does).
- When user enters more rooms, and differentiating is enabled, display a tooltip or bubble pointing to the "Groups" button at the bottom of the screen: "Tap here to find your group rooms"