Docs: circshift!(::AbstractVector, ::Integer) (#57539)

Closes #46016

(cherry picked from commit b0323ab)

Author: barucden

base/abstractarray.jl

@@ -3536,7 +3536,31 @@ function _keepat!(a::AbstractVector, m::AbstractVector{Bool})
     deleteat!(a, j:lastindex(a))
 end
 
-## 1-d circshift ##
+"""
+    circshift!(a::AbstractVector, shift::Integer)
+
+Circularly shift, or rotate, the data in vector `a` by `shift` positions.
+
+# Examples
+
+```jldoctest
+julia> circshift!([1, 2, 3, 4, 5], 2)
+5-element Vector{Int64}:
+ 4
+ 5
+ 1
+ 2
+ 3
+
+julia> circshift!([1, 2, 3, 4, 5], -2)
+5-element Vector{Int64}:
+ 3
+ 4
+ 5
+ 1
+ 2
+```
+"""
 function circshift!(a::AbstractVector, shift::Integer)
     n = length(a)
     n == 0 && return