doc/neubot.1.rst: fix a couple of nits

1) Combining download and upload, the speedtest test and the
   bittorrent test run for about ten (not five) seconds.

2) There's no need to be root to dump / show the content of
   the database.
Replace restructured text english FAQ with markdown english FAQ

I noticed that markdown is better supported by github; therefore, I
migrated the FAQ to simplify my life.

With the fully supported FAQ inside github, now I can stop maintaining
a copy of the faq in neubot's website. Hooray!

I don't have time to migrate the Italian FAQ; therefore, I've added
a note that it needs to be updated and migrated.