doc/Mirrors: fix example rsync command

[sbraz]

Hi,
I discussed that in an email with @codyro and @jonathanspw. Can someone please verify my interpretation here?

R means risk, i.e. "receiver-only include" according to the manual. I believe it was a mistake because these temporary files
should be excluded, not included.

I've added a second commit to remove unnecessary trailing whitespace.

[codyro]

Hi Louis,

I agree with your interpretation and that the command should be updated.

I sent you an e-mail a bit back with why I believe it was setup this way initially:

I believe it was used in the past to help seed releases to mirrors prior to the public announcement.

[sbraz]

I believe it was used in the past to help seed releases to mirrors prior to the public announcement.

Oh right, I think I read the email too quickly and missed this sentence. It makes sense then :)
I've updated my commit message.

[jonathanspw]

I tracked down the original commit when this was changed to 9d2bf75 but I cannot find any context as to why. I don't think it had anything to do with staging of updates.

After more reading of man pages and digging on this I have no clue why we have this and I don't see any reason not to change it - in fact I think we should change it so thank you for bringing this up!