document the numeric argument in srand(rng, filename, n=4)

base/random.jl

@@ -221,12 +221,13 @@ end
 
 """
  srand([rng=GLOBAL_RNG], [seed]) -> rng
+ srand([rng=GLOBAL_RNG], filename, n=4) -> rng
 
 Reseed the random number generator. If a `seed` is provided, the RNG will give a
 reproducible sequence of numbers, otherwise Julia will get entropy from the system. For
 `MersenneTwister`, the `seed` may be a non-negative integer, a vector of `UInt32` integers
-or a filename, in which case the seed is read from a file. `RandomDevice` does not support
-seeding.
+or a filename, in which case the seed is read from a file (`4n` bytes are read from the file,
+where `n` is an optional argument). `RandomDevice` does not support seeding.
 """
 srand(r::MersenneTwister) = srand(r, make_seed())
 srand(r::MersenneTwister, n::Integer) = srand(r, make_seed(n))