Docs sample: clarify that a is an array (#942)

Author: fonsp

src/sampling.jl

@@ -461,7 +461,7 @@ seqsample_d!(a::AbstractArray, x::AbstractArray) = seqsample_d!(default_rng(), a
 
 ### Interface functions (poly-algorithms)
 """
-    sample([rng], a, [wv::AbstractWeights])
+    sample([rng], a::AbstractArray, [wv::AbstractWeights])
 
 Select a single random element of `a`. Sampling probabilities are proportional to
 the weights given in `wv`, if provided.