Nice necro, but it's quite easy.
the text file gives examples, but I'll go through it all using an example from my personal worldgen file.
Code:
UNIFORM golDirt2 3 0 32 8 50 128 true
First you need to specify UNIFORM or NORMAL, tbh, you might as well use UNIFORM. NORMAL is slightly different and increases the concentration of a block at a specific level, bit like a chance graph of /\, while UNIFORM is more --
Next press TAB
Then you need a unique name, I'm adding more dirt, so I called it golDirt2
Next it needs the block and meta ID. Dirt is 3:0 (look in NEI) So thats 3 TAB 0
Next is the Cluster size, which is roughly how many blocks will spawn in a cluster. You can't generate a cluster smaller than 4. That's a limit of the vanilla MC mechanics (KL is making a fix for this in 1.7)
Next is the number of clusters, I'm asking for 8 clusters (or, if you like, 8 attempts at generating clusters)
After that it needs the minimum and maximum Y co-ords for the block. I want this extra dirt to spawn between 50 and 128.
Lastly true just specifies that the block retrogens. Always a good thing.
You need to edit CoFHWorld.cfg:
# This allows for custom generation to be specified in the WorldCustomGen.txt file.
B:AllowCustomGeneration=true
When you load the game, CoFHWorld-Generation.cfg will update from the information from WorldCustomGen.txt in a custom section of the config. I always delete this custom section if I edited WorldCustomGen, just to be on the safe side.
It's easier to edit the txt file then the cfg file.