Bugreport: Everything crashes when running an example from the docstring

Hi here is one example docstring from `pushfirst`
```julia
julia> f(x) = 3x + 2
f (generic function with 1 method)

julia> ir = @code_ir f(1)
1: (%1, %2)
%3 = 3 * %2
%4 = %3 + 2
return %4

julia> pushfirst!(ir, :(println("hello, world")))
%5

julia> ir
1: (%1, %2)
%5 = println("hello, world")
%3 = 3 * %2
%4 = %3 + 2
return %4
```

when running this with `IRTools.func(ir)(f, 1)` everything crashes.
I experience similar behaviour everytime I try to insert literal values like `"hello, world"` in this case.

Probably this is just missing and wrong documentation - What is the current way of inserting literal values?