fix small typo in tutorial doc
//! It can have the following values:
//!
//! - a correct result `Ok((I,O))` with the first element being the remaining of the input (not parsed yet), and the second the output value;
-//! - an error `Err(Err::Error(c))` with `c` an enum that contians an error code with its position in the input, and optionally a chain of accumulated errors;
+//! - an error `Err(Err::Error(c))` with `c` an enum that contains an error code with its position in the input, and optionally a chain of accumulated errors;
//! - an error `Err(Err::Incomplete(Needed))` indicating that more input is necessary. `Needed` can indicate how much data is needed
//! - an error `Err(Err::Failure(c))`. It works like the `Error` case, except it indicates an unrecoverable error: we cannot backtrack and test another parser
//!
