Update docs for vso-agent

Author: Oren Novotny

docs/more-info/build-server-setup/tfs-build-vnext.md

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+# Visual Studio Online (Build vNext) Setup
+## Basic Usage
+In [Visual Studio Online](https://www.visualstudio.com/) build vNext (the web based build system) you can add a build step as follows:
+
+* **Build Step:** Command Line
+	* Might need to fully qualify the path.
+	* Tip: Use a script and/or another command step to call `NuGet Install GitVersion.CommandLine` first so you don't have to check in the exe.
+* **Tool:**  `GitVersion.exe`
+* **Arguments:** `/output buildserver /updateassemblyinfo true`
+
+Then in your build parameters simply [add a placeholder](#nuget-in-teamcity) of the GitVersion variables you would like to use.
+
+GitVersion writes build parameters into VSO, so they will automatically be passed to your build scripts to use.
+
+## GitVersion Build Step for VSO
+Visual Studio Online has support for custom build steps. This is planned but TBD. For now, the command line does work.
+
+ 
+## Running inside TeamCity
+* We output the individual values of the GitVersion version as the build parameter: `GitVersion.*` (Eg: `GitVersion.Major`) if you need access to them in your build script
+
+### NuGet in VSO
+* Add dummy parameter to the project called `GitVersion.NuGetVersion`.
+* Then setup you nuget pack build set the "version" to `%GitVersion.NuGetVersion%`
+
+