doc: Add comment to prevent same error (also now test must catch it)

Author: jhg

src/c.rs

@@ -19,7 +19,7 @@ use super::panic_if_null;
 /// 
 /// If the C string is not a valid UTF-8 string.
 #[must_use]
-#[inline]
+#[inline] // ATTENTION!: 'a lifetime is needed, does NOT REMOVE it, see commit 5a03be91d2da8909986db7c54650f3a7863a91ff fixing 3a1d15f33e8e418ef6bee2b7b9e096780bd2c8ac
 pub unsafe fn ref_str<'a>(string: *const c_char) -> Result<&'a str, Utf8Error> {
     #[cfg(any(feature = "panic-if-null", debug_assertions))]
     panic_if_null(string);