Update doc/specs/stdlib_str2num.md

Co-authored-by: Jeremie Vandenplas <[email protected]>

Author: jalvesz

doc/specs/stdlib_str2num.md

@@ -76,7 +76,7 @@ Return a scalar of numerical type (`integer`, `real32` or `real64`).
 ```fortran
 program example_str2num
     use stdlib_kinds, only: dp
-    use stdlib_str2num
+    use stdlib_str2num, only: to_num_p
     character(:), allocatable, target :: chain
     character(len=:), pointer :: cptr
     real(dp), allocatable :: r(:)