Add note about (un)shift to (push/pop)first docs (#38823)

This would be helpful for new users when searching for these functions
via e.g. apropos().

Author: tckmn

base/array.jl

@@ -1222,6 +1222,8 @@ end
 
 Insert one or more `items` at the beginning of `collection`.
 
+This function is called `unshift` in many other programming languages.
+
 # Examples
 ```jldoctest
 julia> pushfirst!([1, 2, 3, 4], 5, 6)
@@ -1246,6 +1248,8 @@ end
 
 Remove the first `item` from `collection`.
 
+This function is called `shift` in many other programming languages.
+
 # Examples
 ```jldoctest
 julia> A = [1, 2, 3, 4, 5, 6]