fix -D missing_docs

Author: burrbull

Cargo.lock

@@ -552,6 +552,8 @@ impl U32Ext for u32 {
 
 pub fn build_rs() -> TokenStream {
     quote! {
+        //! Builder file for Peripheral access crate generated by svd2rust tool
+
         use std::env;
         use std::fs::File;
         use std::io::Write;