docs: Useful Revsets section looks like runon sentences

[joyously]

https://github.com/martinvonz/jj/blob/5e407982b19793a7e240b2010e837e3b148a973f/docs/github.md?plain=1#L194

When I look at the GitHub page, the Revsets are hard to read.

[ilyagr]

Thanks! It's meant to be a list, but the Markdown isn't formatted correctly.

[martinvonz]

Yes, thanks for reporting it. I'll work on a fix.