You need to make a file called "mapname.arena" with this content:
{
map "mapname"
bots "kyonshi"
longname "Lang map name"
fraglimit 10
type "single ffa tourney sp ctf"
}
The above of course should be changed if you want more bots another default fraglimit or the map is not a ctf/dm/single player map
The file should be placed in the scripts directory inside your pk3-file