fix: docs for reader::first_char now no longer incorrectly state None may be returned

`first_char`'s return type is `char`, not `Option<char>`, so `Option<_>::None` can never be returned

Author: phrohdoh

src/reader.rs

@@ -55,9 +55,6 @@ use std::io::BufRead;
 
 /// Returns the first character of a string slice.
 ///
-/// If `input` is not empty, then its first char will be returned. Otherwise,
-/// `None` is returned.
-///
 /// # Panics
 ///
 /// This function will panic if `input` is an empty string slice.