Merge pull request NuGet#640 from NuGet/anangaur-semver-vs2015

Adding VS 2015+VSIX req for SemVer 2.0.0

Author: Kraig Brockschmidt

docs/Reference/Package-Versioning.md

@@ -91,7 +91,8 @@ For nuget.org, a package is defined as a SemVer v2.0.0 package if either of the
 If you upload a SemVer v2.0.0-specific package to nuget.org, the package is invisible to older clients and available to only the following NuGet clients:
 
 - NuGet 4.3.0+
-- Visual Studio 2017 version 15.3+ 
+- Visual Studio 2017 version 15.3+
+- Visual Studio 2015 with [NuGet VSIX v3.6.0](https://dist.nuget.org/visualstudio-2015-vsix/latest/NuGet.Tools.vsix)
 - dotnet.exe (.NET SDK 2.0.0+)
 
 Third-party clients: