Add a short discussion of string concatenation to the FAQ.

Rationale: even though JuliaLang#11030
was closed, there is discussion of the issue from time to time on
Github and the forum; so if any question is frequently asked, this is.

doc/src/manual/faq.md

@@ -593,6 +593,12 @@ julia> remotecall_fetch(anon_bar, 2)
 1
 ```
 
+### Why does Julia use "*" for string concatenation? Why not "+" or something else?
+
+The main argument against `+` is that string concatenation is not commutative, while `+` is generally used as a commutative operator. While the Julia community recognizes that other languages use different operators and `*` may be unfamiliar for some users, syntax choices always have a subjective element and further discussions about this operator have not turned out to be productive, so it is not likely to change in the short run.
+
+Note that you can also use `string(...)` to concatenate strings (and other values converted to strings); similarly, `repeat` can be used instead of `^` to repeat strings. The [interpolation syntax](@ref string-interpolation) is also useful for constructing strings.
+
 ## Packages and Modules
 
 ### What is the difference between "using" and "import"?