[mergebot] Amend messages for land checks (#82649)
### Description
<!-- What did you change and why was it needed? -->
We forgot that the < was for comments in markdown. Also added a link to the wiki to the start land checks message so users can see why their PR is taking extra time to land.
### Issue
<!-- Link to Issue ticket or RFP -->
n/a
### Testing
<!-- How did you test your change? -->
n/a
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82649
Approved by: https://github.com/janeyx99, https://github.com/ZainRizvi
