Make nuget package solution-level

[cd21h]

Please remove readme.md from content folder of nuget package.

[ggreig]

Just wanted to add my support to this request. It's a significant frustration for us, as we want our internal project level package to depend on MSBuildTasks. And it confuses our source control system - it notices the file being added, then complains it can't be found when it comes to committing changes, because Delete-Temporary-File in Install.ps1 removes it again!