Correcting docs for building in Linux (dotnet#58)

* Correcting docs for building in linux

Related to: dotnet#57

* Adding more description

* Providing link for further information

* Improving docs

* Making less ubuntu centric.

* Adding pre-req link for macOS

* Improving sentences

Author: maryamariyan

Documentation/building/unix-instructions.md

@@ -7,37 +7,44 @@ Building ML.NET on Linux and macOS
 3. Navigate to the `machinelearning` directory
 4. Run the build script `./build.sh`
 
-Calling the script `build.sh` builds both the native and managed code.
+Calling the script `./build.sh` builds both the native and managed code.
 
-For more information about the different options when building, run `build.sh -?` and look at examples in the [developer-guide](../project-docs/developer-guide.md).
+For more information about the different options when building, run `./build.sh -?` and look at examples in the [developer-guide](../project-docs/developer-guide.md).
 
 ## Minimum Hardware Requirements
 - 2GB RAM
+- x64
 
-## Prerequisites (native build)
+## Prerequisites
 
 ### Linux
 
-First, the package lists might need to be updated
+The following components are needed:
 
-`sudo apt-get update`
+* git
+* clang-3.9
+* cmake 2.8.12
+* libunwind8
+* curl
+* All the requirements necessary to run .NET Core 2.0 applications: libssl1.0.0 (1.0.2 for Debian 9) and libicu5x (libicu52 for ubuntu 14.x, libicu55 for ubuntu 16.x, and libicu57 for ubuntu 17.x). For more information on prerequisites in different linux distributions click [here](https://docs.microsoft.com/en-us/dotnet/core/linux-prerequisites?tabs=netcore2x).
 
-On Linux, the following components are needed
+e.g. for Ubuntu 16.x:
 
-* CMake on the PATH
-* Clang 3.5+ (same requirements as coreclr/corefx)
-* All the requirements necessary to run .NET Core 2.0 applications
-* libunwind
-* curl
+```sh
+sudo apt-get update
+sudo apt-get install git clang-3.9 cmake libunwind8 curl
+sudo apt-get install libssl1.0.0 libicu55
+```
 
 ### macOS
 
 macOS 10.12 or higher is needed to build dotnet/machinelearning.
 
 On macOS a few components are needed which are not provided by a default developer setup:
-* CMake
+* cmake 3.10.3
+* All the requirements necessary to run .NET Core 2.0 applications. To view macOS prerequisites click [here](https://docs.microsoft.com/en-us/dotnet/core/macos-prerequisites?tabs=netcore2x).
 
 One way of obtaining CMake is via [Homebrew](http://brew.sh):
 ```sh
 $ brew install cmake
-```
+```