docs: state that password is taken in from stdin

Author: joelsa

README.md

@@ -20,6 +20,8 @@ cargo binstall argon2-cli
 echo -n "password" | argon2
 ```
 
+This CLI accepts the password via `stdin`, which avoids putting the password in shell history.
+
 ### Options
 
 ```
@@ -57,7 +59,7 @@ echo -n "password" | argon2 somesalt -e
 
 ## Compatibility
 
-This CLI strives for interface compatibility with the [C reference implementation](https://github.com/P-H-C/phc-winner-argon2), but does not guarantee it. Deviations are made where the original interface significantly hinders usability. For example, the salt is optional in our implementation and a cryptographically secure random salt is generated by default.
+This CLI strives for interface compatibility with the [C reference implementation](https://github.com/P-H-C/phc-winner-argon2), but does not guarantee it. Deviations are made where the original interface significantly hinders usability. For example, the salt is optional in our implementation and a cryptographically secure random salt is generated by default. This CLI also accepts the password via `stdin`, unlike the standard Linux `argon2` CLI, which helps avoid leaking passwords into shell history.
 
 ## License