go(bench): explain what Neighbourhood const is for

bench/bench.go

@@ -9,6 +9,8 @@ type funcParams struct {
 }
 
 const (
+	// Neighbourhood is the number of neighbouring values that are to be
+	// generated as part of e.g. Stochastic Hill Climbing algo.
 	Neighbourhood = 10
 	// MaxFES is the maximum number of allowed function evaluations.
 	MaxFES = 10000