Place xml files in %TEAMCITY%\config\projects\%Project%\pluginData\metaRunners
(e.g. C:\ProgramData\JetBrains\TeamCity\config\projects\BaBuildServer\pluginData\metaRunners
)
If you're using the 'DNX - Install and configure DNX' meta runner, the Build Agent must feature the configuration property %teamcity.tool.nuget%
pointing to the directory that contains the nuget.exe.
This DNX Meta Runners for Teamcity is based on a package of meta runners for K. Unfortunately I can't find the original github repository anymore, so I can't credit the original creator here. If you have any leads, just contact me or submit a pull request.