chore: document preferred language for scanner

docs/section-3-creating-parsers.md

@@ -626,6 +626,9 @@ grammar({
 
 Then, add another C or C++ source file to your project. Currently, its path must be `src/scanner.c` or `src/scanner.cc` for the CLI to recognize it. Be sure to add this file to the `sources` section of your `binding.gyp` file so that it will be included when your project is compiled by Node.js and uncomment the appropriate block in your `bindings/rust/build.rs` file so that it will be included in your Rust crate.
 
+> **Note**
+> While it is possible to write an external scanner in C++, it can be difficult to get working cross-platform and introduces extra requirements; therefore it is *greatly* preferred to use C.
+
 In this new source file, define an [`enum`][enum] type containing the names of all of your external tokens. The ordering of this enum must match the order in your grammar's `externals` array; the actual names do not matter.
 
 ```c