README: update

README.md

@@ -0,0 +1,18 @@
+# filecrypt-rs
+
+Cli tool in Rust to encrypt and decrypt files with an Ascon-Keccak AEAD.  
+The PBKDF is not yet implemented and is just SHA256(password) for now
+
+## Commands
+
+### Encrypt a file
+
+```bash
+filecrypt-rs encrypt --input <FILE> --output <FILE> --password <PASSWORD>
+```
+
+### Decrypt a file
+
+```bash
+filecrypt-rs decrypt --input <FILE> --output <FILE> --password <PASSWORD>
+```