Consider including how to switch repository mirrors in the documentation

[ralphy]

It would be good to document somewhere (maybe in the Help Manual) how to switch and use a different Linux Lite repository.

/litemanual/software.html#sources explains how to "Change your Software Updates Country Location" but that does not apply to the Linux Lite repository. It doesn't really help much if there are different mirrors for the Linux Lite repository but everyone keeps on using the default one. As Linux Lite user base grows, requests to master server will increase substantially over time. It is helpful for the master server and most importantly for end-users to use a LL mirror closer to them other than repo.linuxliteos.com.