Improve docstring of BallSearch and KBallSearch

Author: juliohm

src/neighborsearch/ball.jl

@@ -5,7 +5,9 @@
 """
     BallSearch(domain, ball)
 
-A method for searching neighbors in `domain` inside `ball`.
+A method for searching neighbors in `domain` inside metric `ball`.
+
+See [`MetricBall`](@ref) for additional details.
 """
 struct BallSearch{D<:Domain,B<:MetricBall,T} <: NeighborSearchMethod
   # input fields

src/neighborsearch/kball.jl

@@ -6,7 +6,9 @@
     KBallSearch(domain, k, ball)
 
 A method that searches `k` nearest neighbors and then filters
-these neighbors using a norm `ball`.
+these neighbors using a metric `ball`.
+
+See [`MetricBall`](@ref) for additional details.
 """
 struct KBallSearch{D<:Domain,B<:MetricBall,T} <: BoundedNeighborSearchMethod
   # input fields