Updated /mwe howplaygame

[William0216]

• This adds the arguments hpg and explain, because howplaygame is long and explain should be more memorable.
• This changes the message to include more information, particularly about:
  • How to obtain diamonds and diamond armor, which is frequently asked by new players
  • The new damage-to-win mechanic
• This acknowledges that information in the linked guide is outdated (the last update was 4 years ago)
• This says "Before the walls fall", instead of "During the first 6 minutes" which resolves Issue #59 without adding Faceoff detection logic. This should be fine because the leaderboard already says how long it takes for the walls to fall, making the previous text redundant (and 30 seconds off even in the normal mode).