Small update to macro keyword doc (#34305)

Note that macros can accept varargs but not kwargs

Author: quinnj

base/docs/basedocs.jl

@@ -158,7 +158,8 @@ resulting expression is substituted directly into the program at the point where
 the macro is invoked.
 Macros are a way to run generated code without calling [`eval`](@ref Base.eval), since the generated
 code instead simply becomes part of the surrounding program.
-Macro arguments may include expressions, literal values, and symbols.
+Macro arguments may include expressions, literal values, and symbols. Macros can be defined for
+variable number of arguments (varargs), but do not accept keyword arguments.
 
 # Examples
 ```jldoctest
@@ -169,6 +170,14 @@ julia> macro sayhello(name)
 
 julia> @sayhello "Charlie"
 Hello, Charlie!
+
+julia> macro saylots(x...)
+           return :( println("Say: ", \$(x...)) )
+       end
+@saylots (macro with 1 method)
+
+julia> @saylots "hey " "there " "friend"
+Say: hey there friend
 ```
 """
 kw"macro"