README.md in noise-ruby-0.5.3 vs README.md in noise-ruby-0.6.0

@@ -27,9 +27,14 @@
     $ ./autogen.sh
     $ ./configure --enable-experimental --enable-module-ecdh --enable-module-recovery --enable-benchmark=false
     $ make
     $ sudo make install
 
+In addition, libsodium is required.
+
+    $ brew install libsodium
+
+
 Add this line to your application's Gemfile:
 
 ```
 gem 'noise-ruby'
 ```