docs: update docs

README.md

@@ -9,31 +9,27 @@ Code implemented according to the spec described in
 
 ## Features
 
-* `secure_random` (default: `on`): Enable secure RNG when generating padding bytes for tc_tea.
+* `random` (default: `on`): Enable RNG when generating padding bytes for tc_tea.
+* `random_secure` (default: `on`): Use a _secure_ RNG when generating padding bytes for tc_tea.
+
+If you don't expect to encrypt anything, you can specify `default-features = false` to drop RNG support.
+In this case, it will use a [pre-generated deterministic salt](https://xkcd.com/221/).
 
 ## Install
 
 Add the following to `[dependencies]` section in your `Cargo.toml` file:
 
 ```toml
-tc_tea = "0.1.4"
+tc_tea = "0.2"
 ```
 
-## Troubleshooting
-
-* Key need to have `16` bytes or more.
-  * `None` will be returned if less than `16` bytes provided.
-  * If more bytes were provided, only the first 16 bytes will be used.
-* Encrypted data should have a size that is multiple of 8.
-  * `None` will be returned if `encrypted_data.len() % 8 > 0`.
-
 ## Usage
 
 ```rust
 use tc_tea;
 
 fn hello_tc_tea() {
-    let key = "12345678ABCDEFGH";
+    let key = b"12345678ABCDEFGH";
     let encrypted = tc_tea::encrypt(&"hello", &key).unwrap();
     let decrypted = tc_tea::decrypt(&encrypted, &key).unwrap();
     assert_eq!("hello", std::str::from_utf8(&decrypted).unwrap());
@@ -49,4 +45,5 @@ SPDX-License-Identifier: MIT OR Apache-2.0
 ```
 
 [tc_tea_cpp]: https://github.com/TarsCloud/TarsCpp/blob/a6d5ed8/util/src/tc_tea.cpp
+
 [tc_tea_spec]: https://github.com/iweizime/StepChanger/wiki/%E8%85%BE%E8%AE%AFTEA%E5%8A%A0%E5%AF%86%E7%AE%97%E6%B3%95