Adjust leveldbXXX description (according to weed/storage/volume_loading.go)

Optimization.md

@@ -6,8 +6,8 @@ When starting volume server, you can specify the index type. By default it is us
 `weed volume -index=leveldb` can change to leveldb. It is much faster to start up a volume server, at the cost of a little bit slower when accessing the files. Compared to network speed, the extra cost is not that much in most cases.
 
 Note: there are 3 flavors of leveldb indexes for the volume server:
-- `leveldb`: small memory footprint (4MB total, 1 write buffer, 3 block buffers)
-- `leveldbMedium`: medium memory footprint (8MB total, 3 write buffers, 5 block buffers)
+- `leveldb`: small memory footprint (4MB total, 1 write buffer, 2 block buffers)
+- `leveldbMedium`: medium memory footprint (8MB total, 2 write buffers, 4 block buffers)
 - `leveldbLarge`: large memory footprint (12MB total, 4 write buffers, 8 block buffers)
 
 ## Preallocate volume file disk spaces