add NEWS item, improve help text

NEWS.md

@@ -77,6 +77,10 @@ Library improvements
     (to alter Windows command-line generation) and `windows_hide` (to
     suppress creation of new console windows) ([#13780]).
 
+  * Statistics:
+
+    * Improve performance of `quantile` ([#14413]).
+
 Deprecated or removed
 ---------------------
 

base/docs/helpdb.jl

@@ -2977,13 +2977,6 @@ with empty collections (see ``reduce(op, itr)``).
 """
 mapreduce(f, op, itr)
 
-doc"""
-    quantile!(v, p)
-
-Like `quantile`, but overwrites the input vector.
-"""
-quantile!
-
 doc"""
     accept(server[,client])
 

base/statistics.jl

@@ -515,7 +515,7 @@ median{T}(v::AbstractArray{T}, region) = mapslices(median!, v, region)
 """
     quantile!([q, ] v, p; sorted=false)
 
-Compute the quantile(s) of a vector `v` at the probabilities `p`, outputting into array `q`. `sorted` indicates whether `v` can be assumed to be sorted; if it is `false` (the default), then the elements of `v` may be partially sorted in the process.
+Compute the quantile(s) of a vector `v` at the probabilities `p`, with optional output into array `q` (if not provided, a new output array is created). The keyword argument `sorted` indicates whether `v` can be assumed to be sorted; if `false` (the default), then the elements of `v` may be partially sorted.
 
 The elements of `p` should be on the interval [0,1], and `v` should not have any `NaN` values.
 """
@@ -586,7 +586,7 @@ end
 """
     quantile(v, p; sorted=false)
 
-Compute the quantile(s) of a vector `v` at a specified probability or vector `p`.
+Compute the quantile(s) of a vector `v` at a specified probability or vector `p`. The keyword argument `sorted` indicates whether `v` can be assumed to be sorted
 
 The `p` should be on the interval [0,1], and `v` should not have any `NaN` values.
 """