message: Update README with passphrase autogeneration
diff: @@ -45,12 +45,14 @@ $ rage -o example.png.age -r age1uvscypafkkxt6u2gkguxet62cenfmnpc0smzzlyun0lzszf
  ### Passphrases
  -Files can be encrypted with a passphrase by using `-p/--passphrase`.
  +Files can be encrypted with a passphrase by using `-p/--passphrase`. By default
  +rage will automatically generate a secure passphrase.
  ```bash
  $ rage -p -o example.png.age example.png
  -Type passphrase: [hidden]
  -Confirm passphrase:
  +Type passphrase (leave empty to autogenerate a secure one): [hidden]
  +Using an autogenerated passphrase:
  + kiwi-general-undo-bubble-dwarf-dizzy-fame-side-sunset-sibling
  $ rage -d -p example.png.age >example.png
  Type passphrase: [hidden]
  ```
  