Move man page into the normal source
Move man page into the normal source

It was in the debian packaging branch. Now that the script is called
btrfs-heatmap in here, the man page also makes sense.

Also put it in section 1 instead of 8. It's just a normal utility, not
some super special system management command.

Fixes: https://github.com/knorrie/btrfs-heatmap/issues/11

knorrie/btrfs-heatmap