Add wiki note about game length limit

[eduherminio]

Type of pull request:

• [ ] Bug fix
• [ ] Feature
• [x] Other

Description:

As suggested in #983, this adds a note to the Wiki about the max. game length limit and how reaching it without deliverying checkmate forces a draw

Related Issues:

Checklist:

• [x] I have read and followed the contribution guidelines.
• [x] I have added necessary documentation (if applicable).
• [ ] The changes pass all existing tests.

Screenshots/logs (if applicable):

[AttackingOrDefending]

I think we should also mention that this is caused by lichess and not lichess-bot.

[eduherminio]

I think we should also mention that this is caused by lichess and not lichess-bot.

Good point, I added an extra sentence clarifying that.