Add optional feature description in Readme, bump version to v1.7.1

Cargo.lock

@@ -1230,7 +1230,7 @@ dependencies = [
 
 [[package]]
 name = "shadowsocks-rust"
-version = "1.7.0"
+version = "1.7.1"
 dependencies = [
  "base64 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "byte_string 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "shadowsocks-rust"
-version = "1.7.0"
+version = "1.7.1"
 authors = ["Y. T. CHUNG <zonyitoo@gmail.com>"]
 description = "shadowsocks is a fast tunnel proxy that helps you bypass firewalls."
 repository = "https://github.com/zonyitoo/shadowsocks-rust"

README.md

@@ -16,6 +16,16 @@ shadowsocks is a fast tunnel proxy that helps you <del>bypass firewalls</del>.
 
 ## Build & Install
 
+### Optional Features
+
+* `sodium` - Enabled linking to [`libsodium`](https://github.com/jedisct1/libsodium), which will also enable ciphers that depending on `libsodium`.
+
+* `rc4` - Enabled `rc4` encryption algorithm. Some OpenSSL Crypto does not ship with `rc4`, because it was already deprecated in 2015.
+
+* `single-threaded` - Let `sslocal` and `ssserver` run in single threaded mode (by using `tokio::current_thread::Runtime`).
+
+Default features: `["sodium", "rc4"]`.
+
 ### **crates.io**
 
 Install from [crates.io](https://crates.io/crates/shadowsocks-rust):