Dependencies in README (#3162)

README.md

@@ -56,7 +56,14 @@ We recommend installing Rust through [rustup](https://www.rustup.rs/). If you do
 	```bash
 	$ curl https://sh.rustup.rs -sSf | sh
 	```
+	
+	Parity also requires `gcc`, `g++` and `make` packages to be installed.
+- OSX:
+	```bash
+	$ curl https://sh.rustup.rs -sSf | sh
+	```
 
+	`clang` and `make` are required. These come with Xcode command line tools or can be installed with homebrew.
 - Windows
 
     Make sure you have Visual Studio 2015 with C++ support installed. Next, download and run the rustup installer from