As in gardening, seeding is where you scatter some seeds (add lots of small bits of content) and hope they will grow into plants (long articles).
So, the idea is to get a very brief piece of information down about different parts of the game. For example, a page about each character which can be expanded by others once they find the wiki. Having lots of articles will help people find the wiki through Google.
It's also useful to add some structure by making [[List of waepons]], [[List of characters]], etc and linking to all the possible pages, even if you don't create all those yourself.
See also MeatBall:SeedPosting