Adding instructions specific for OS X (#899)

* Adding instructions specific for OS X

* fix link format

* fix link format

* adding mac libraries and how to start testnet

* adding bullets to make it more clear

* typo

substrate/README.adoc

@@ -129,9 +129,18 @@ rustup update nightly
 rustup target add wasm32-unknown-unknown --toolchain nightly
 rustup update stable
 cargo install --git https://github.com/alexcrichton/wasm-gc
-sudo apt install cmake pkg-config libssl-dev git
 ----
 
+You will also need to install the following packages:
+
+ - Linux:
+[source, shell]
+sudo apt install cmake pkg-config libssl-dev git
+
+ - Mac:
+[source, shell]
+brew install cmake pkg-config openssl git
+
 Then, grab the Substrate source code:
 
 [source, shell]
@@ -158,6 +167,10 @@ You can start a development chain with:
 [source, shell]
 cargo run -- --dev
 
+Or you can join the BBQ Birch Testnet with:
+[source, shell]
+cargo run
+
 include::doc/packages/packages.adoc[]
 
 include::CONTRIBUTING.adoc[leveloffset=+1]