Fix table of contents (#980)

* Fix table of contents

* fix ToC reference due to merge

Author: bergmeister

README.md

@@ -14,10 +14,8 @@ Table of Contents
 - [Installation](#installation)
     + [From PowerShell Gallery](#from-powershell-gallery)
       - [Supported PowerShell Versions and Platforms](#supported-powerShell-versions-and-platforms)
-        * [Windows](#windows)
-        * [Linux (*Tested only on Ubuntu 14.04*)](#linux-tested-only-on-ubuntu-1404)
     + [From Source](#from-source)
-      - [Requirements](#requirements-1)
+      - [Requirements](#requirements)
       - [Steps](#steps)
       - [Tests](#tests)
 - [Suppressing Rules](#suppressing-rules)
@@ -86,6 +84,8 @@ Exit
 
 ### From Source
 
+#### Requirements
+
 * [.NET Core 2.1.101 SDK](https://www.microsoft.com/net/download/dotnet-core/sdk-2.1.101) or newer
 * [PlatyPS 0.9.0 or greater](https://github.com/PowerShell/platyPS/releases)
 * Optionally but recommended for development: [Visual Studio 2017](https://www.visualstudio.com/downloads/)