Update cmd/gpio/src/lib.rs

Co-authored-by: Matt Keeter <matt@oxide.computer>

Author: lzrd

cmd/gpio/src/lib.rs

@@ -74,7 +74,7 @@
 //! Port K    0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
 //! ```
 //! To get input values with STM32H753 GPIO configuration settings,
-//! use the `--with-config` or `-w` flag with --input:
+//! use the `--with-config` or `-w` flag with `--input`:
 //!
 //! ```console
 //! $ humility gpio --input -with-config --pins B:0,B:14,E:1