Specific build instructions for mac vs linux

CONTRIBUTING.md

@@ -8,31 +8,57 @@ We're happy you want to contribute! You can help us in different ways:
 
 ### Getting and building
 
-1.  Install the following prerequisites, as necessary:
-  - A C compiler. On Mac OS X, Xcode should suffice.
-  - PostgreSQL development libraries
+#### Mac
+
+1. Install XCode
+3. Install packages with homebrew
 
    ```bash
-    # on mac
-    brew install postgresql
-
-    # on linux
-    apt-get install libpq-dev
+   brew install git postgresql-9.5`
+   brew link openssl --force`
    ```
 
-  - Git 1.8+
-
-2.  Get the code
+4. Get the code
 
    ```bash
    git clone https://github.com/citusdata/citus.git
    ```
 
-3.  Build and test
+5. Build and test
 
    ```bash
+   cd citus
    ./configure
    make
-   make install
+   sudo make install
+   cd src/test/regress
+   make check
+   ```
+
+#### Linux
+
+1. Install a C compiler and Git 1.8+
+2. Install PostgreSQL 9.5 ([instructions](http://www.postgresql.org/download/))
+3. Install packages
+
+   ```bash
+   # Ubuntu
+   apt-get install postgresql-server-dev-9.5 libreadline-dev
+   ```
+
+4. Get the code
+
+   ```bash
+   git clone https://github.com/citusdata/citus.git
+   ```
+
+5. Build and test
+
+   ```bash
+   cd citus
+   ./configure
+   make
+   sudo make install
+   cd src/test/regress
    make check
    ```